SIM Card A Subscriber Identity Module or Subscriber Identification Module (SIM) is an integrated circuit chip that is intended to securely store the International Mobile Subscriber Identity (IMSI) number and its related key. SIM Circuit The SIM circuit is part of the function of a Universal Integrated Circuit Card (UICC) physical smart card, which is usually made of PVC with embedded contacts and semiconductors. "SIM cards" are designed to be transferable between di erent mobi...