# SIM - Subscriber Identity Module A Subscriber Identity Module (SIM) card is a small electronic chip that is used to identify and authenticate a mobile device on a cellular network. It is inserted into the device and contains information such as the phone number, the International Mobile Subscriber Identity (IMSI), and the Authentication Key (Ki). The SIM card consists of a small microcontroller, non-volatile memory, and other passive components. The microcontroller is responsible for managing the SIM's functionality and communication with the mobile device. The non-volatile memory stores the data and information that is needed for the SIM card to operate. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://sim-cards.learn-telecom.com/gsm-identifiers/sim-subscriber-identity-module.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.