Mobile phone SIM card for use with MTN network in Cameroon, bought in Buea, Cameroon, 2012.

SIM cards are a crucial to making a mobile phone work. This example was purchased by Science Museum staff on a trip to Cameroon in 2012. It enabled the staff members to use a mobile phone on the MTN mobile network, one of two commercial network providers operating in Cameroon at the time. SIM stands for 'Subscriber Identity Module', and is a key part of GSM, an international agreement about the technical standards used by mobile phones. GSM originated in a handful of European companies, but soon spread around the world.