SIM

    A Subscriber Identity Module (SIM) is part of a removable smart card ICC (Integrated Circuit Card), also known as SIM Cards, for mobile cellular telephony devices such as mobile computers and mobile phones. SIM cards securely store the service-subscriber key (IMSI) used to identify a subscriber. The SIM card allows users to change phones by simply removing the SIM card from one mobile phone and inserting it into another mobile phone or broadband telephony device.

SIM cards are available in two standard sizes. The first is the size of a credit card (85.60 mm × 53.98 mm x 0.76 mm). The newer, more popular miniature-version has a width of 25 mm, a height of 15 mm, and a thickness of 0.76 mm. However most SIM cards are supplied as a full-sized card with the smaller card held in place by a few plastic links and can be easily broken off to be used in a phone that uses the smaller SIM.

The first SIM Card was made in 1991, with Munich smart card maker Giesecke & Devrient selling the first 300 SIM cards to Finnish wireless network operator Elisa Oyj (formerly Radiolinja). W-SIM is a SIM card which also integrates core cellular technology into the card itself.


Uses:

    The use of SIM cards is mandatory in GSM devices. The equivalent of a SIM in UMTS is called the Universal Subscriber Identity Module (USIM), whereas the Removable User Identity Module (RUIM) is more popular in CDMA-based devices. Many CDMA-based standards do not include any such card, and the service is bound to a unique identifier contained in the handset itself.

The Satellite phone networks Iridium (satellite), Thuraya and Inmarsat's BGAN also use SIM cards. Sometimes these SIM cards work in regular GSM phones and also allows GSM customers to roam in satellite networks by using their own SIM card in a satellite phone.