SIM Card

A SIM card is a card with a chip, which is used in mobile radio technology to identify a mobile device and its unique mobile phone number within its network. The acronym SIM is short for the technical term 'Subscriber Identity Module'. Regardless of the price plan (prepaid or contract), mobile network providers give their customers a SIM card for mobile data transmission and/or voice communication.

To protect against unauthorised use, the cards are usually protected by a PIN that must be entered directly after the mobile phone is switched on, in order to activate the card. After several incorrect attempts to enter the PIN a PUK (Personal Unblocking Key) is required to unlock the card. If the PUK is entered incorrectly a number of times, the card is permanently blocked and has to be replaced.