November 25, 2011 at 16:21Poking around in a SIM card: processor, memory, file system + I / O
It is difficult to find a person who does not know what a SIM card or Subscriber Identity Module is - a subscriber identity module. This piece of plastic with golden contacts on one of the surfaces is the key to the services provided by the mobile operator. And inside the SIM-card there is a specialized computer with quite complex functionality.
A SIM card is actually one of the varieties of a more general entity - a processor “smart card” (Smart Card).
The processor in the body of the SIM card
Such "smart cards" can be used for various purposes:
In CDMA networks, R-UIM - Removable User Identity Module is used to identify subscribers. The word Removable (replaceable) emphasizes its new status, because earlier, in IS-95 networks (the communication standard on the basis of which CDMA networks worked in the USA, Russia and other countries, for example, SONET in Moscow), elements identifying the subscriber were placed among electronic phone components. Obviously, the use of R-UIM greatly simplifies the replacement of the phone when it malfunctions or when buying a new one, and allows you to use a phone of a different standard in roaming.
But then we will talk about subscriber identity modules used in GSM-UMTS networks, which by tradition will be called SIM or cards.
Currently, three formats of GSM-UMTS subscriber identity modules are standardized.
Three formats of GSM-UMTS
ID-1 UICC subscriber identity modules — the very first option — are the size of a regular bank card. Many people remember it by the models of the 90s - Motorola 8900, StarTAC and others. Currently, the new models of mobile terminals are practically not used due to the large size.
UICC plug-in is the most common format now. Typically, such modules are broken out from cards of size ID-1 by cuts made during manufacture.
Mini-UICC is the card format that Apple began to use in iPhone 4, iPad, iPad 2. Now, other manufacturers of mobile phones and other devices intend to produce models in which it will be necessary to insert modules of this format. Sometimes this format is called 3FF, or colloquially “micro-SIM”. And these cards are usually broken out from an ID-1 format card. The reasons for the appearance of such a variety are obvious - saving space inside the phone.
They try not to make a universal cut-out that allows, at the user's choice, to break out a plug-in or a mini-UICC module from the plastic of an ID-1 card, for reasons of reliability - when trying to break a card into a plug-in format, it is very easy to damage the remaining thin jumpers, after which the plug-in card will not be securely held in the phone.
ID-1 card with a “universal” slot for Plug-in and Mini-UICC
A shift of the SIM card in the holder threatens problems with the phone. Minimal trouble - the phone just does not feel the presence of SIM and is not registered on the network. In the worst case scenario, it can happen, as if the wires were mixed up - voltage spill at the wrong address and short circuit with unpredictable consequences.
Manufacturers of mobile terminals who are active, who are less resolute, usually object to the use of adapters that are advertised for using Mini-UICC cards in phones designed for Plug-in cards. The adapter is slightly thicker than the plug-in, and in addition, slots at the junction of the card and the adapter can break the contacts in the phone when installing the SIM, depriving the user of a chance of warranty repairs.
In some devices operating in a mobile network (navigators, devices for controlling the location of vehicles, etc.), subscriber identification modules can simply be soldered in the form of microcircuits, but ordinary subscribers usually do not encounter such modules.
In everyday life, there are modules with a different pattern of the contact pad and a different number of contacts. Some manufacturers use the "corporate" design of the contact pad as their business card.
The standards provide 8 positions for platforms through which the modules are connected to mobile terminals, but not all of them are always used. Often there are cards with 6 contacts, and the rest of the metallized part is usually connected to the "ground".
Cards with 6 and 8 contacts
Used contacts:
C1 - Vcc - power;
C2 - Reset - contact management card;
C3 - CLK - Clock - clock frequency;
C5 - general ("earth");
C6- Vpp - programming voltage, which is used when recording service information
C7 - I / O - line of the serial input / output interface.
The standards provide for the use of C4 and C8 contacts in the mode of exchanging information with the mobile terminal in USB mode, which provides a higher speed of information transfer than through the usual I / O SIM interface.
In practice, now the USB interface mode is not actually used, since equipment with this interface is practically not manufactured and is not ordered by consumers, therefore these contacts, even if they are on the card, are connected to ground. In the future, work through the I / O interface line will be discussed.
Comparing the electronic contents of SIM with a computer (especially with a pocket one), you can find many elements that are identical in function:
There are differences - something that is not in the module:
For more information about the architecture and production of SIM, see this topic .
The amount of memory that can be used to store information in SIM can be different and gradually grows as technology develops. A few years ago there was a flash of euphoria from the advent of technology that allows you to place gigabytes of information in SIM. It was then that after a heated discussion in the industry and two rounds of voting in the GSM Association, the USB standard was chosen for working with large volumes of information. But then the euphoria subsided, and now there are not so many mobile terminals on the market that can work with such SIMs, and SIMs themselves with a gigabyte memory are not in great demand among operators.
And why do we need large amounts of memory for SIM cards and what amounts of memory are really needed?
SIM memory is used for several purposes:
It is also obvious that increasing the amount of memory increases the cost of SIM, and so now operators, most often, try to limit themselves to the volumes minimally necessary to accommodate the necessary information.
In addition to the fact that the phone or other mobile terminal provides the SIM card with power and a clock signal, it is fully responsible for the exchange of information between devices - the phone always acts as a master, and the card is always a slave.
The phone sends commands / requests to the SIM, and the SIM only answers them, accompanying the responses with information about the response status.
In the status information, the card can confirm that the command was completed successfully, ask for additional time to prepare an answer, report errors of various types, or inform that it has special information for the phone that it can receive by sending a special request for selection in the next command .
This mechanism for transferring information from a card to a phone is usually called the SIM (or Card) Application Toolkit, STK. It is used to implement various services, which are based on application programs (usually written in JavaCE - Java Card Edition), executed inside SIM. In the phones menu, with installed SIM-cards of the main operators, you can find items and entire menu trees formed on the basis of information provided by applications working in SIM-cards.
The work of real-time services, for example, constantly providing information on the current balance, is based on the same technology.
It is possible to organize roaming for small companies by switching two IMSIs in one card - one corresponding to its network, and the other - provided “on loan” by another operator - “big brother”. For example, Beeline networks operating in the CIS countries use the Dual IMSI mechanism to provide roaming services to their subscribers. In their SIM-cards one IMSI of their network is registered, and the other IMSI, corresponding to the Russian Beeline network. In the Russian Beeline network, these IMSI are reserved in the HLR for the provision of roaming services to "subsidiary" companies and communication channels are organized with them. A Beeline subscriber from a “subsidiary” company, being, for example, in a European country, switches the SIM operating mode to roaming using the STK menu. As a result, a phone with such a SIM card appears for a roaming network, as belonging to a subscriber of the Russian Beeline network. Then everything happens, as usual, only the Russian Beeline network organizes the transfer of information on behalf of the "subsidiary" network.
You can even organize a WEB server inside SIM! So, if someone is confused by the “slave position” of SIM, he may well consider it a server.
After turning on and starting the operating system, the phone supplies Vcc to the SIM. The standards provide for three SIM voltage ratings - 5V, 3V and 1.8V.
Previously, cards were issued that could only work at a voltage of 5V. After the appearance of phones that supplied a voltage of no more than 3V to the card, these old SIMs were gradually replaced by new ones capable of working from 3V, which can withstand work in phones that provide 5V.
Since phones that provide SIM cards with a voltage of only 1.8V have not yet been encountered, modern SIM cards do not create compatibility problems due to supply voltages.
After the telephone is powered, the clock signal is applied, and after the stable mode is established, the voltage on the Reset contact rises. This serves as a signal for the SIM card to start working with it, to which it responds with a sequence of bytes called ATR (Answer To Reset).
ATR bytes contain basic information about card capabilities and supported communication protocols. In particular, he can tell the phone possible options for accelerating the exchange of information through the interface by increasing the clock frequency and speed of information transfer.
After reading the information from ATR, the phone can start the PPS (Protocol and Parameter Selection) procedure for coordinating the mode of exchanging phone information with the card. If the phone is not able to find an option that is acceptable for him and for SIM, then communication with the card will continue in default mode (at a speed of 9600 bps).
In such cases, subscribers often complain about the too long reading of the phone book from the SIM card to the phone, for some reason, reproaching the operator who issued the SIM card.
In the process of switching on, the SIM card and the mobile terminal (telephone) exchange “business cards”. The phone reads from the SIM file containing the SST - SIM Service Table - encoded information about the STK functions that the SIM can perform in a certain way. In turn, the phone sends to the SIM card TERMINAL PROFILE - in a certain way encoded information about which communication functions with SIM it can support. As a result, both parties receive information about the partner’s abilities and can interact correctly when implementing services based on STK.
SIM has a multi-level hierarchical file structure with access control.
Access to files is regulated by the need for the user to present different types of access codes.
Some of these access codes are well known - this is Personal Identification Numbers - PIN (aka PIN1) and PIN2. Other codes are used for administrative access to service files.
What makes this distinction? An activated PIN request allows you to secure money on your personal account associated with the SIM card against unauthorized use by unauthorized persons.
Another important security technique is, for example, the inability to read information from certain files, for example, reading the Ki key, which is used in various cryptographic algorithms to authenticate the subscriber and generate traffic encryption keys.
A few years ago, at a round table on the prospects of smartphones organized by one of the manufacturers, one of the participants complained to me that Beeline lacks a service that is very useful for parents. He wanted parents to limit the ability of their children to call only a certain set of phone numbers — home, parents, grandparents, and the child should not call other numbers.
Imagine his surprise when I showed him the work of the FDN function - Fixed Dialing Numbers, which is implemented by the combined actions of the phone and SIM card. Allowed numbers using the phone are simply written to a specific SIM card file, and access to change this list is blocked using PIN2. After that, a phone with such a SIM will refuse to call numbers not listed on the FDN list.
True, it should be noted that not all phones support the operation of this service.
The skin of the fingers is covered with organic fatty acids, which upon contact cause corrosion of metal parts. Small details are just about the contacts of the SIM card.
In the photo there is a laser pointer, the surface of which, after quite rare use, has lost several layers of a metal coating - chromium plating and copper plating just because of these fatty acids! As you know, “radio engineering is the science of contacts”, but SIM has a lot of them!
Laser pointer, affected by fatty acids on the fingers
Such a fate should not befall the SIM card contacts, but for this you need to protect the SIM contacts from pollution by all means, and try not to touch them with your fingers!
If there is a problem with the contacts between the phone and SIM, then neat cleaning of the contacts with a soft eraser can help. Just do not need to clean the crumbs from the contacts with your fingers after the cleaning operation, otherwise all problems will start again! It’s better to simply blow them off or rinse them off gently with alcohol.
Once, a subscriber came to the Beeline office, who was sent from the phone repair service to change the SIM card, because his completely new phone turned off spontaneously during a call, balance check, sending SMS.
I had to explain to him that turning off the phone has no connection with the health of the SIM. Using an eraser, I carefully cleaned the contacts on the battery and in the phone, after which the phone began to work normally. Along the way, I gave the subscriber a small lecture on hygiene.
Of course, not in all cases the situation is so obvious, and to determine who is to blame - the phone or SIM that the services do not work, is not easy - because their communication is almost intimate. It is especially important to understand the causes of conflicts when developing new services using STK or when detecting SIM incompatibility problems with some models of phones or other mobile terminals.
In such cases, an analyzer of information exchange protocols on the interface of a SIM terminal provides an invaluable service: An
analyzer of information exchange protocols between a SIM and a mobile terminal.
Instead of a SIM card, a special probe is inserted into the terminal, and the SIM is connected via a flexible cable. During operation, all information about events occurring on the interface is recorded in the memory of a computer connected to the analyzer.
Comparison of the information collected with the requirements of the standards allows you to unambiguously and convincingly establish the party to the conflict.
Of course, only some features of SIM-cards and their work in phones are affected in the material, but if there is interest in this topic, just ask questions, I will answer in detail.
PS Today Boomboorum wrote another review of our office .
SIM-card is the same processor credit card, but in profile
A SIM card is actually one of the varieties of a more general entity - a processor “smart card” (Smart Card).
The processor in the body of the SIM card
Such "smart cards" can be used for various purposes:
- Identification of mobile subscribers.
- Providing access to encrypted content of various paid systems, for example, television.
- Like bank cards
- For identification of the user who is granted access to corporate networks, etc.
In CDMA networks, R-UIM - Removable User Identity Module is used to identify subscribers. The word Removable (replaceable) emphasizes its new status, because earlier, in IS-95 networks (the communication standard on the basis of which CDMA networks worked in the USA, Russia and other countries, for example, SONET in Moscow), elements identifying the subscriber were placed among electronic phone components. Obviously, the use of R-UIM greatly simplifies the replacement of the phone when it malfunctions or when buying a new one, and allows you to use a phone of a different standard in roaming.
But then we will talk about subscriber identity modules used in GSM-UMTS networks, which by tradition will be called SIM or cards.
Face off cards?
Currently, three formats of GSM-UMTS subscriber identity modules are standardized.
Three formats of GSM-UMTS
ID-1 UICC subscriber identity modules — the very first option — are the size of a regular bank card. Many people remember it by the models of the 90s - Motorola 8900, StarTAC and others. Currently, the new models of mobile terminals are practically not used due to the large size.
UICC plug-in is the most common format now. Typically, such modules are broken out from cards of size ID-1 by cuts made during manufacture.
Mini-UICC is the card format that Apple began to use in iPhone 4, iPad, iPad 2. Now, other manufacturers of mobile phones and other devices intend to produce models in which it will be necessary to insert modules of this format. Sometimes this format is called 3FF, or colloquially “micro-SIM”. And these cards are usually broken out from an ID-1 format card. The reasons for the appearance of such a variety are obvious - saving space inside the phone.
They try not to make a universal cut-out that allows, at the user's choice, to break out a plug-in or a mini-UICC module from the plastic of an ID-1 card, for reasons of reliability - when trying to break a card into a plug-in format, it is very easy to damage the remaining thin jumpers, after which the plug-in card will not be securely held in the phone.
ID-1 card with a “universal” slot for Plug-in and Mini-UICC
A shift of the SIM card in the holder threatens problems with the phone. Minimal trouble - the phone just does not feel the presence of SIM and is not registered on the network. In the worst case scenario, it can happen, as if the wires were mixed up - voltage spill at the wrong address and short circuit with unpredictable consequences.
Manufacturers of mobile terminals who are active, who are less resolute, usually object to the use of adapters that are advertised for using Mini-UICC cards in phones designed for Plug-in cards. The adapter is slightly thicker than the plug-in, and in addition, slots at the junction of the card and the adapter can break the contacts in the phone when installing the SIM, depriving the user of a chance of warranty repairs.
In some devices operating in a mobile network (navigators, devices for controlling the location of vehicles, etc.), subscriber identification modules can simply be soldered in the form of microcircuits, but ordinary subscribers usually do not encounter such modules.
How many contacts should be?
In everyday life, there are modules with a different pattern of the contact pad and a different number of contacts. Some manufacturers use the "corporate" design of the contact pad as their business card.
The standards provide 8 positions for platforms through which the modules are connected to mobile terminals, but not all of them are always used. Often there are cards with 6 contacts, and the rest of the metallized part is usually connected to the "ground".
Cards with 6 and 8 contacts
Used contacts:
C1 - Vcc - power;
C2 - Reset - contact management card;
C3 - CLK - Clock - clock frequency;
C5 - general ("earth");
C6- Vpp - programming voltage, which is used when recording service information
C7 - I / O - line of the serial input / output interface.
The standards provide for the use of C4 and C8 contacts in the mode of exchanging information with the mobile terminal in USB mode, which provides a higher speed of information transfer than through the usual I / O SIM interface.
In practice, now the USB interface mode is not actually used, since equipment with this interface is practically not manufactured and is not ordered by consumers, therefore these contacts, even if they are on the card, are connected to ground. In the future, work through the I / O interface line will be discussed.
Where did they stick the computer?
Comparing the electronic contents of SIM with a computer (especially with a pocket one), you can find many elements that are identical in function:
- Processor (CPU);
- RAM (RAM);
- Permanent memory for storing the operating system ROM (ROM);
- Memory for storing user information;
- File system;
- I / O controller
There are differences - something that is not in the module:
- Human interface elements that the module simply does not need.
- Power source (using terminal power)
- Clock generator (similarly, supply from the terminal).
For more information about the architecture and production of SIM, see this topic .
The amount of memory that can be used to store information in SIM can be different and gradually grows as technology develops. A few years ago there was a flash of euphoria from the advent of technology that allows you to place gigabytes of information in SIM. It was then that after a heated discussion in the industry and two rounds of voting in the GSM Association, the USB standard was chosen for working with large volumes of information. But then the euphoria subsided, and now there are not so many mobile terminals on the market that can work with such SIMs, and SIMs themselves with a gigabyte memory are not in great demand among operators.
Can I store HD movies on SIM cards?
And why do we need large amounts of memory for SIM cards and what amounts of memory are really needed?
SIM memory is used for several purposes:
- Storage of information that is vital for the phone to work with this SIM in a mobile network. For example, this is IMSI - International Mobile Subscriber Identity - a sequence of numbers that not only identifies a specific SIM and its owner, but also indicates which operator from which country released it. This information helps roaming quickly figure out where to find out what services can be provided by phone with this card, because the first three digits of IMSI are the country code, and the next two digits are the network code (in the Americas the network code consists of three digits). This is Ki - a secret key that provides an opportunity for the network to make sure that it is really their “own” SIM card, and not some scammer uses someone else's IMSI to gain access to services. Plus files for storing other service information.
- Storage of user information . Usually, the phonebook and received SMSs are placed on the cards. In cards for the UMTS network, a phone book can have significantly more functionality than just a list of names and their corresponding phone numbers. You can attach several numbers to a name, add an email address and other information. However, due to the development of the same functions in the phones themselves, these SIM capabilities are practically not used.
- Placement of application files that can run in the built-in SIM virtual Java-machine and provide some services. If the operator actively uses services based on applications running in the SIM card, this part may occupy the most significant part of the card memory.
It is also obvious that increasing the amount of memory increases the cost of SIM, and so now operators, most often, try to limit themselves to the volumes minimally necessary to accommodate the necessary information.
Who drives whom?
In addition to the fact that the phone or other mobile terminal provides the SIM card with power and a clock signal, it is fully responsible for the exchange of information between devices - the phone always acts as a master, and the card is always a slave.
The phone sends commands / requests to the SIM, and the SIM only answers them, accompanying the responses with information about the response status.
In the status information, the card can confirm that the command was completed successfully, ask for additional time to prepare an answer, report errors of various types, or inform that it has special information for the phone that it can receive by sending a special request for selection in the next command .
This mechanism for transferring information from a card to a phone is usually called the SIM (or Card) Application Toolkit, STK. It is used to implement various services, which are based on application programs (usually written in JavaCE - Java Card Edition), executed inside SIM. In the phones menu, with installed SIM-cards of the main operators, you can find items and entire menu trees formed on the basis of information provided by applications working in SIM-cards.
The work of real-time services, for example, constantly providing information on the current balance, is based on the same technology.
It is possible to organize roaming for small companies by switching two IMSIs in one card - one corresponding to its network, and the other - provided “on loan” by another operator - “big brother”. For example, Beeline networks operating in the CIS countries use the Dual IMSI mechanism to provide roaming services to their subscribers. In their SIM-cards one IMSI of their network is registered, and the other IMSI, corresponding to the Russian Beeline network. In the Russian Beeline network, these IMSI are reserved in the HLR for the provision of roaming services to "subsidiary" companies and communication channels are organized with them. A Beeline subscriber from a “subsidiary” company, being, for example, in a European country, switches the SIM operating mode to roaming using the STK menu. As a result, a phone with such a SIM card appears for a roaming network, as belonging to a subscriber of the Russian Beeline network. Then everything happens, as usual, only the Russian Beeline network organizes the transfer of information on behalf of the "subsidiary" network.
You can even organize a WEB server inside SIM! So, if someone is confused by the “slave position” of SIM, he may well consider it a server.
How does it turn on and why does it slowly load a book?
After turning on and starting the operating system, the phone supplies Vcc to the SIM. The standards provide for three SIM voltage ratings - 5V, 3V and 1.8V.
Previously, cards were issued that could only work at a voltage of 5V. After the appearance of phones that supplied a voltage of no more than 3V to the card, these old SIMs were gradually replaced by new ones capable of working from 3V, which can withstand work in phones that provide 5V.
Since phones that provide SIM cards with a voltage of only 1.8V have not yet been encountered, modern SIM cards do not create compatibility problems due to supply voltages.
After the telephone is powered, the clock signal is applied, and after the stable mode is established, the voltage on the Reset contact rises. This serves as a signal for the SIM card to start working with it, to which it responds with a sequence of bytes called ATR (Answer To Reset).
ATR bytes contain basic information about card capabilities and supported communication protocols. In particular, he can tell the phone possible options for accelerating the exchange of information through the interface by increasing the clock frequency and speed of information transfer.
After reading the information from ATR, the phone can start the PPS (Protocol and Parameter Selection) procedure for coordinating the mode of exchanging phone information with the card. If the phone is not able to find an option that is acceptable for him and for SIM, then communication with the card will continue in default mode (at a speed of 9600 bps).
In such cases, subscribers often complain about the too long reading of the phone book from the SIM card to the phone, for some reason, reproaching the operator who issued the SIM card.
"Hi who are you?"
In the process of switching on, the SIM card and the mobile terminal (telephone) exchange “business cards”. The phone reads from the SIM file containing the SST - SIM Service Table - encoded information about the STK functions that the SIM can perform in a certain way. In turn, the phone sends to the SIM card TERMINAL PROFILE - in a certain way encoded information about which communication functions with SIM it can support. As a result, both parties receive information about the partner’s abilities and can interact correctly when implementing services based on STK.
File system and security
SIM has a multi-level hierarchical file structure with access control.
Access to files is regulated by the need for the user to present different types of access codes.
Some of these access codes are well known - this is Personal Identification Numbers - PIN (aka PIN1) and PIN2. Other codes are used for administrative access to service files.
What makes this distinction? An activated PIN request allows you to secure money on your personal account associated with the SIM card against unauthorized use by unauthorized persons.
Another important security technique is, for example, the inability to read information from certain files, for example, reading the Ki key, which is used in various cryptographic algorithms to authenticate the subscriber and generate traffic encryption keys.
Why it is useful to read instructions
A few years ago, at a round table on the prospects of smartphones organized by one of the manufacturers, one of the participants complained to me that Beeline lacks a service that is very useful for parents. He wanted parents to limit the ability of their children to call only a certain set of phone numbers — home, parents, grandparents, and the child should not call other numbers.
Imagine his surprise when I showed him the work of the FDN function - Fixed Dialing Numbers, which is implemented by the combined actions of the phone and SIM card. Allowed numbers using the phone are simply written to a specific SIM card file, and access to change this list is blocked using PIN2. After that, a phone with such a SIM will refuse to call numbers not listed on the FDN list.
True, it should be noted that not all phones support the operation of this service.
Wash your hands before eating.
The skin of the fingers is covered with organic fatty acids, which upon contact cause corrosion of metal parts. Small details are just about the contacts of the SIM card.
In the photo there is a laser pointer, the surface of which, after quite rare use, has lost several layers of a metal coating - chromium plating and copper plating just because of these fatty acids! As you know, “radio engineering is the science of contacts”, but SIM has a lot of them!
Laser pointer, affected by fatty acids on the fingers
Such a fate should not befall the SIM card contacts, but for this you need to protect the SIM contacts from pollution by all means, and try not to touch them with your fingers!
If there is a problem with the contacts between the phone and SIM, then neat cleaning of the contacts with a soft eraser can help. Just do not need to clean the crumbs from the contacts with your fingers after the cleaning operation, otherwise all problems will start again! It’s better to simply blow them off or rinse them off gently with alcohol.
Change or not change?
Once, a subscriber came to the Beeline office, who was sent from the phone repair service to change the SIM card, because his completely new phone turned off spontaneously during a call, balance check, sending SMS.
I had to explain to him that turning off the phone has no connection with the health of the SIM. Using an eraser, I carefully cleaned the contacts on the battery and in the phone, after which the phone began to work normally. Along the way, I gave the subscriber a small lecture on hygiene.
Of course, not in all cases the situation is so obvious, and to determine who is to blame - the phone or SIM that the services do not work, is not easy - because their communication is almost intimate. It is especially important to understand the causes of conflicts when developing new services using STK or when detecting SIM incompatibility problems with some models of phones or other mobile terminals.
In such cases, an analyzer of information exchange protocols on the interface of a SIM terminal provides an invaluable service: An
analyzer of information exchange protocols between a SIM and a mobile terminal.
Instead of a SIM card, a special probe is inserted into the terminal, and the SIM is connected via a flexible cable. During operation, all information about events occurring on the interface is recorded in the memory of a computer connected to the analyzer.
Comparison of the information collected with the requirements of the standards allows you to unambiguously and convincingly establish the party to the conflict.
Of course, only some features of SIM-cards and their work in phones are affected in the material, but if there is interest in this topic, just ask questions, I will answer in detail.
PS Today Boomboorum wrote another review of our office .