SIM (Subscriber Identity Module) is part of a removable integrated circuit smart card known as a SIM Card. They are used in mobile phones and mobile computers using hone connections to securely store the service-subscriber key (IMSI) used in identifying a subscriber. Since the SIM identifies the subscriber, not the device, a user can change phones by removing the SIM card from one mobile phone and inserting it into another mobile phone or broadband telephony device.