GSM

The Global system for mobile communications (GSM) is a world-wide standard for digital wireless telephones. The standard is open, non-propiertary and still evolving. It has obtained wide support especially in Europe, where it is the major standard.

GSM differs from its predecessors most significantly in that it is completely digital. It has also been designed for sufficient security.

Yeah, ok, it's a start. Please, add some more

GSM exists in three main versions, based on the band used: GSM-900, GSM-1800 and GSM-1900. GSM-900 (900 Mhz) and GSM-1800 (1.8 Ghz) are used in most of the world, excluding the United States (and Canada?). The United States uses GSM-1900 (1.9 Ghz) instead, since in the U.S. the 900 and 1800 bands were already allocated.