Sim Card

A Subscriber Identity Module (SIM) on a removable SIM Card securely stores the service-subscriber key (IMSI) used to identify a subscriber on mobile telephony devices (such as computers and mobile phones). 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. The use of SIM cards is mandatory in GSM devices. The equivalent of a SIM in UMTS is called the Universal Integrated Circuit Card (UICC), which runs a USIM application, whereas the Removable User Identity Module (R-UIM) is more popular in CDMA-based devices. The UICC card is still colloquially referred to as a SIM-card. Many CDMA-based standards do not include any such card, and the service is bound to a unique identifier contained in the handset itself.

SIM operating systems come in two main types: Native and Java Card. Native SIMs are based on proprietary, vendor specific software whereas the Java Card SIMs are based on standards, particularly Java Card which is a subset of the Java programming language specifically targeted at embedded devices. Java Card allows the SIM to contain programs that are hardware independent and interoperable. Each SIM is Internationally identified by its ICC-ID (Integrated Circuit Card ID). ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization. The ICCID is defined by the ITU-T recommendation E.118. The number is up to 18 or 19 digits long and in addition is often associated with a single check digit calculated using the Luhn algorithm.

A Universal Subscriber Identity Module is an application for UMTS mobile telephony running on a UICC smart card which is inserted in a 3G mobile phone. There is a common misconception to call the UICC card itself a USIM, but the USIM is merely a logical entity on the physical card. It stores user subscriber information, authentication information and provides storage space for text messages and phone book contacts. The phone book on a UICC has been greatly enhanced.