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. 

It is possible to duplicate a SIM card by accessing its key and storing it in multiple cards.

How does a SIM card work?

  • SIM cards are designed according to the ISO/IEC 7816 international standard maintained by the International Organisation for Standardisation and the International Electrotechnical Commission.