GSM stands for Global System for Mobile Communication and is the most popular 2G mobile phone standard in the world.
GSM is used by about 80% of all mobile phones - approximately 2 billion people across more than 212 countries.
The widespread use of the GSM standard has made it easy for most mobile phone users to use their phones overseas thanks to roaming agreements between operators using the same GSM standard.
GSM - then labelled Groupe Spécial Mobile was originally conceived back in 1982 as a European standard for mobile phones. The first GSM network went live in 1992 in Finland.
GSM introduced the concept of the SIM card (Subscriber Identity Module card) - a detachable smart card that lets users swap their phone number and contacts between handset.