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 What is a SIM card?

  • SIM stands for ‘Subscriber Identification Module’.

  • It is an integrated circuit, or a microchip, that identifies the subscriber on a given network.

  • Individulas are identified by a number, called the international mobile subscriber identity (IMSI). 

  • The SIM card is a subscriber’s ID card in the city. When someone wants to contact a subscriber in this city, the network uses the subscriber’s SIM card to find them and confirm their identity.

  • In order for a mobile phone to connect to any cellular network that follows the Global System for Mobile Communications (GSM) standard, a SIM card is mandatory. 

What is a SIM card?

This relationship is established using a unique authentication key — a piece of data that a user needs to ‘unlock’ access to the network. 

Every SIM card stores this data and it is designed such that the user can’t access it through their phone.