The Subscriber Identity Module is a smartcard that is necessary to make use of a mobile phone. The SIM is the key used to identify and authenticate the mobile subscriber. On the SIM is also memory available for personalised data, such as a telephone book and messages.

The subscriber is identified with an IMSI, International Mobile Subscriber Identity, and a telephone number.

The SIM made a clear seperation between a mobile phone and a subscriber possible. The subscriber can make use of any mobile phone under his own account if the SIM card is put in the phone.

De chip van een SIM.

There are two different sizes available, a credit card size and a small size that is of the size of he chip that is on most credit cards. Nearly all phones use the small version.

The use of a SIM can be guarded with a PIN code from 4 to 8 digits. If 4 times the wrong PIN code is typed, the SIM will be blocked. To unblock the SIM the PUK (PIN Unblocking Key) is needed. This is an 8 digit code that is known by the authorised user and given by the service provider.

Nowadays, there is also an embedded SIM (eSIM) available.

See also