How Do SIM Cards Work? Each SIM card holds a user's IMSI (International Mobile Subscriber Identity) and ICCID (Integrated Circuit Card Identifier) information. Mobile network operators use a SIM card's IMSI and ICCID to verify the holding user and decide whether to grant network access to the associated device.

A SIM card slot is the place where the SIM card is inserted into the device. The SIM card slot is typically located on the side or bottom of the device and can be easily opened with a small tool, such as a paper clip or SIM card ejector tool. The SIM card slot is used to insert or remove the SIM card from the device.