As of 2015, a SIM card is used by a GSM cell phone to connect to a subscribed mobile network. The average SIM card is made up of two components, which are the Subscriber Identity Module and the plastic encasement that surrounds it.
Inside the SIM card is unique data that allows a mobile network to identify a phone. The SIM card gives the network access to communication features, such as phone calls and SMS messaging. A SIM card also contains a small-sized memory space, which allows it to save up to 250 unique contacts as well as other types of information. SIM cards are interchangeable between different compatible handsets.