Subscriber Identity Module

The Subscriber Identity Module (SIM) is a small smart card which contains both programming and information. In GSM networks, the A3 and A8 algorithms are implemented in the Subscriber Identity Module. Subscriber information, such as the IMSI (International Mobile Subscriber Identity), is stored in the SIM. The Subscriber Identity Module (SIM) can also be used to store user-defined information such as phonebook entries. One of the advantages of the GSM architecture is that the SIM may be moved from one Mobile Station to another. This makes upgrading mobile telephhones very simple for the GSM user.