What does SIM mean?
A Subscriber Identity Module (SIM) is a removable smart card, available in two standard sizes. The first the size of a credit card (85.60 mm × 53.98 mm x 0.76 mm), while its more popular mini version has a width of 25 mm, a height of 15 mm, and a thickness of 0.76 mm. SIM cards store securely the key identifying a mobile phone service subscriber.
The SIM card allows users to change phones easily by removing the SIM card and inserting it into another mobile phone, thereby eliminating the need for activation of the new mobile phone on the network. The use of SIM card is mandatory in the GSM world. The equivalent of a SIM in UMTS is called the Universal Integrated Circuit Card (UICC), whereas the Removable User Identity Module (RUIM) is more popular in the CDMA world.
