GSM - Global System for Mobile Communications is the world's most popular standard for mobile telephone systems. GSM differs from its predecessor technologies in that both signaling and speech channels are digital, and thus GSM is considered a second generation (2G) mobile phone system. This also facilitates the wide-spread implementation of data communication applications into the system.
GSM has been continuously developed. For example, release 97 added packet data GPRS. Release 99 has introduced a high-speed data transmission - EDGE
GSM refers to the networks of the second generation (2 Generation), although in 2010 suspended in a phase of 2,75 G due to numerous extensions (1G - analog cellular, 2G - digital cellular, 3G - wideband digital cellular, dial multi-purpose computer networks including the Internet). Cell phones are available for four frequency bands: 850 MHz, 900 MHz, 1800 MHz and 1900 MHz.