A SIM (subscriber identity module) card contains information that allows cell phone carriers to identify a phone and for subscribers to store data and settings. SIM cards make it possible to transfer information from one cell phone to another.
Most SIM cards contain an International Mobile Subscriber Identity number and a Mobile Subscriber Integrated Services Digital Network number. The IMSI number identifies each subscriber to the cell phone carrier and contains three groups of numbers. The MSISDN number is simply the subscriber's telephone number.
Most SIM cards allow users to store contact information, including names and numbers, that can be transferred from one phone to another, usually while upgrading to a newer phone. To protect against theft or unauthorised installation, SIM cards also contain a personal identification number.
Short Message Service messages received and saved are also stored on a SIM card. Text messaging uses the SMS, but does not save outgoing text messages.