We’ve all heard the debate between Unlocked GSM Cell Phones and CDMA phones. The biggest difference is that GSM Cell Phones carry a SIM Card. But what is a SIM Card? SIM stands for Subscriber Identity Module. It allows users to change phones while maintaining all information from their previous phone. All the user must do is transfer the card from one phone to another.

Each SIM card contains a unique serial number. It is this serial number that enables your phone, or SIM Card, to be tracked. The card also contains the international unique number of the mobile user (IMSI), security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to and two passwords (PIN for usual use and PUK for unlocking). This in addition to all the information the user stores on the phone such as contacts and calendar. The IMSI, each of which is unique, is coded and read as the first three digits represent the Mobile Country Code (MCC), the next two digits represent the Mobile Network Code (MNC) and the next ten digits represent the mobile station identification number.

SIM Cards are available in two standard sizes. The first is a credit card size but the newer and much more common fit is a width of 25 mm, a length of 15 mm and a thickness of 0.76 mm. Both of these can fit into any Unlocked GSM Cell Phones and sometimes the card will be the credit card size with the smaller one built into it. It of course is removable from the larger unit.

Today there are many third-party businesses that offer the SIM lock removal from phones. By having such a service done to your phone it may now be used on any network by simply placing a new SIM Card on it. This is a very popular action today as people are liberated from binding contracts as well as penalty fees for leaving their current service provider.

The SIM card is a device that has truly differentiated GSM Cell Phones from CDMA phones. It allows users to keep their information as stated above and freely move to a new phone if they desire. On the flipside they allow us to get Unlocked GSM Cell Phones and simply get a new SIM card, giving us the freedom to move from service provider to service provider. And what a novel concept that is.

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