SIM Cards

SIM Cards

A SIM (subscriber identity module) is an electronic card which securely stores the key identifying a mobile phone service subscriber, as well as subscription information, preferences and text messages. The equivalent of a SIM in UMTS is a Universal Subscriber Identity Module (USIM).

The SIM stores network state information such as its current location area identity (LAI). If the handset is turned off and back on again it will take data off the SIM and search for the LAI it was in. This saves time by avoiding having to search the whole list of frequencies that the telephone normally would. Each SIM is uniquely identified by its ICCID [International Circuit Card ID].
SIM cards identify users uniquely by holding an IMSI.

What is a SIM card?
The SIM (Subscriber Identification Module or Subscriber Identity Module) card - a.k.a. "smart card" - holds all of a subscriber's personal information and phone settings. In essence, it is the subscriber's authorization to use the network. It also holds the phone number, personal security key and other data necessary for the handset to function. The card can be switched from phone to phone, letting the new phone receive all calls to the subscriber's number.

How do SIM cards functions?
The SIM is inside each handset and functions as its digital brain. The authentication and encryption capabilities of the SIM prevent your phone from being stolen and your calls from being eavesdropped on. The SIM's digital memory, which stores information like your rate plan, phone number and service features, also allows you to easily personalize your service and contains user ID and billing information that can be switched between different phones. So, with your SIM card installed, you can make or receive calls personally even when you're using a borrowed phone. Upgrading your phone is as simple as slipping your SIM card into your new phone.


In July 2005, the Finnish government announced that a Citizen Certificate - a government-guaranteed 'electronic identity' included in a SIM card - will be made available to every individual resident in Finland before the end of 2005, allowing mobile phone users to access e-services on the move. The Citizen Certificate has been described as "basically an e-ID card that will be compatible with several hardware devices, such as mobile phones, PDAs, personal computers, Digital TV sets, and public web kiosks".
[1] The first SIM cards with embedded Citizen Certificates have already been made available in selected localities.
The use of SIM card is mandatory in the GSM world, whereas the SIM (RUIM) is not very popular in the CDMA world.
The major SIM card vendors in the market are Axalto, Gemplus, G&D and Oberthur Card Systems.
W-SIM is a SIM card which also integrates core cellular technology into the card itself.