What is a sim card?
SIM is short for Subscriber Identity Module. A sim card is a tiny, removable card smaller than a credit card which is fitted into GSM cell phones at the time of signing on as a subscriber. The small encoded circuit board on the card stores mobile phone data such as contact names and numbers, SMSs Text Messages and security information.
A SIM card is a removable memory card and can be put into any compatible GSM handset, permitting the user to keep the same number while changing handsets. It is a standard unique chip which is a must in every GSM cell phone.
SIM cards are used with carriers that operate on the Global System for Mobile Communication (GSM) network. The competing network is Code Division Multiple Access (CDMA), a technology created by U.S. company Qualcomm. As of fall 2005, CDMA cell phones and CDMA carriers do not support SIM cards in most parts of the world, though this is changing. A CDMA SIM card called the R-UIM (Re-Useable Identification Module) was made available in China in 2002, and will eventually be available worldwide. Expectations for the future include a cell phone market that supports both SIM (GSM) and R-UIM (CDMA) cards by default.