|A small, stamp-size "smart card" used in a GSM phone.
The SIM card contains a microchip that stores data that identifies the caller to the network service provider. The data is also used to encrypt voice and data transmissions, making it nearly impossible to listen in on calls.
The SIM can also store phone book information - phone numbers and associated names.
The SIM, typically located under the battery, can easily be removed and placed in another phone. This will cause the new phone to instantly operate using the subscriber's existing phone number and account.