GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services. GSM is a circuit-switched system that divides each 200 kHz channel into eight 25 kHz time-slots. In addition to using TDMA as its multiple access technique, the system also utilises FDMA, assigning different frequencies between cells. GSM supports data transfer speeds of up to 9.6 kbps, allowing the transmission of basic data services such as SMS text messages.
Enhancements came in 2000 with the introduction of GPRS (General Packet Radio Service) improving data rates to 56–114 kbps, and EDGE (Enhanced Data rates for GSM Evolution) in 2003 which achieves 473 kbps (although 384 kbps is often quoted).