SIM (subscriber identity module)

A card inserted into a GSM/TDMA or GSM-only handset containing subscriber-related data. The card contains 18 digits for GSM markets and 20 digits for TDMA markets. (Cingular)

A Subscriber Identity Module is a card commonly used in a GSM phone. The card holds a microchip that stores information and encrypts voice and data transmissions, making it close to impossible to listen in on calls. The SIM card also stores data that identifies the caller to the network service provider. Your SIM card contains all the information about your phone, such as phone number, phone book information, account, etc. so that you access the wireless network and use your phone's features. This card comes from your wireless service provider. (Nokia)

The Subscriber Identification Module card is a removable memory card that fits into the back of a mobile phone and contains the user's identity code and relevant personal data. The card can be plugged into any GSM compatible handset, instantly personalising it to the user. (Motorola)

A small printed circuit board that must be inserted in any GSM-based mobile phone when signing on as a subscriber. It contains subscriber details, security information and memory for a personal directory of numbers. (Ericsson)