Since buy phone need a two years

contract so people have to use AT&T for

two year. it’s binded with A T & T, and those

monthly plans are quite expensive.People alreay pay at&T with two years contrct no matter they like or dont like they need wait for contract finish then they can chose other phone service supplyers like T mobile or others. actually there are not too many other choice.

And sim unlock card can solve this problem.

1.sim card

SIM card（Subscriber Identity Module） is a wisdom car that conforms to the GSM standard , The SIM card can be inserted in any conform to the GSM standard mobile phone.The function of telephone number along with card not stochastic realized .But Call cost then includes automatically holds in the card user’s bill, has nothing to do with the handset.

2. In the SIM card preserves the data may induce into following four kind of types:

(1) System primary data stores which by the SIM card production manufacturer.

(2) By GSM network operation department or other management department when card provide for user pours into network parameter and user data.Including:

* Warning power and encryption information Ki(Kc One of algorithm input parameters: Dense spoon number)

* A3：IMSI Authentication algorithm

* A5：Adds the dense spoon production algorithm

* A8：Before dense spoon (Kc) production, user dense spoon (Kc) production algorithm

(3) Data stores which by user.For instance, the Short Message, the fixed digit dialing, shrink the position digit dialing, the performance parameter, the speech spend the register and so on.

(4) The user in uses in the card process to store automatically with the renewal network connection and the user information class data.Including recent position registration time handset in position area identification number (LAI), establishment periodic position renewal time interval, temporary mobile subscriber number (TMSI) and so on.

These data all deposit in respective table of contents item, the first kind of data places the root directory, after power source opening first enters the root directory, again enters the correlation according to the instruction the child directory, each kind of table of contents internal data field has respective identification code protection extremely, only then the process checkup distinction will later be able to carry on the inquiry to in the data field data, the read-out and the renewal.

The above first kind of data usually is the permanent data, will pour into later by the SIM card production manufacturer to be unable to change, the second kind of data only then the network movement department’s specialized agency in will only then allow to consult and to renew, again third, four kind of data majority of permission user will use any handset to carry on to it reads/writes the operation.

3. SIM card structure

(1) The SIM card can store up how many telephone number to be decided by the card EEPROM capacity(Has 2K, 3K, the 8K capacity)

If has the 8KB storage capacity, may supply to store up following information:

*100 group of telephone numbers and corresponding natural famous writing;

*15 groups of short informations (Short Message);

*Above 25 groups allocated recently number;

*4 SIM card password (PIN)

(2) The SIM card has the microprocessor chip card, In has 5 modules, each module corresponds a function: CPU (8), program memory ROM(6-16kbit), working storage RAM(128-256kbit), data-carrier storage EEPROM(2-8kbit) and serial communication unit, These 5 module integration in an integrated circuit.The SIM card in connects with the handset time,

needs 5 ties at least:

* Power source（Vcc）

* Clock（CLK）

*Data I/Q（Data）

* Replacement（RST）

* Ground terminal（GND）

4. The GSM network registers the step:

(1) After the handset starting can read IMSI from the SIM card (15 numerals) and TMSI (4 bytes);

(2) When the handset will register the network, will be able IMSI or TMSI issues the network;

(3) The network judges this IMSI or TMSI is effective, must produce 128bit RAND, then issues the handset;

(4) After the handset receives RAND, issues RAND the SIM card;

(5) SIM as the key carries on the A3A8 operation take inside KI to RAND, produces (SRES+Kc);

(6) The handset reads (SRES+Kc)(32bit+64bit), and issues SRES the network;

(7) Network carry on a A3A8 operation, if the result and the

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