Since its creation in around 1990, the SIM card has undergone several transformations in its size (standard, nano, pico SIM), features and uses. Initially, it was simply intended to guarantee the security of electronic communications by supplying the identity of the mobile telephone user and the brand of the terminal provider. Subsequently, greater flexibility was introduced to enable users to keep the same terminal while being able to call different operators.
SIM card (2G)
The SIM card, standardized by the ETSI, was introduced with GSM mobile telephony. It brought with it the equipment and software required for its features. In GSM, the SIM card is the property of mobile operators. It has a number to identify the mobile subscriber internationally (IMSI, International Mobile Subscriber Identity) as well as the reference numbers required for subscriber authentication. Without a SIM card, the GSM user could not connect to a mobile network and would not be able to make or receive phone calls.
SIM cards enable the activities of mobile virtual network operators (MVNO), which use the resources of a network operator in the absence of their own network (around 10% of subscribers).
USIM card (3G)
For convenience, the functions of SIM cards in 3G mobile telephony (UMTS) are shared between the equipment (represented by the Universal Integrated Circuit Card (UICC)) and the software (Universal Subscriber Identity Module (USIM)). The USIM brings improvements ...