GSM, a 2G technology, is the de facto European standard for digital cellular telephone service, and it is also available in the Americas. GSM is the most widely used of the three digital wireless telephone technologies (TDMA, GSM and CDMA), and it supports voice, data, text messaging and cross-border roaming. The SIM (Subscriber Identification Module), a removable plastic card that contains a users data, is an essential element in a GSM network.

GSM operates in multiple frequency bands, GSM 900, GSM 1800, GSM 1900. When GSM is working on a radio frequency of 1800 MHz, it is sometimes referred to as DCS 1800, GSM1800 or PCN.

• 2G
• CDMA
• TDMA
• PCS