Subscriber Identity Module. A tiny chip inserted into a cellular-enable mobile device that stores information about the device. This information can include the cellular provider, the device’s country of origin, and a unique user ID. The information on a Subscriber Identity Module. A tiny chip inserted into a cell... card is how your cellular provider knows what to charge you each month. There are three sizes of SIM cards—standard, micro, and nano. Nano SIM is used today on most mobile phones.