The Global System for Mobile communications is a digital cellular communications system. It was developed in order to create a common European mobile telephone standard but it has been rapidly accepted worldwide. GSM was designed to be compatible with ISDN services.

The idea of cell-based mobile radio systems appeared at Bell Laboratories (in USA) in the early 1970s. However, mobile cellular systems were not introduced for commercial use until the 1980s. During the early 1980s, analog cellular telephone systems experienced a very rapid growth in Europe, particularly in Scandinavia and the United Kingdom. Today cellular systems still represent one of the fastest growing telecommunications systems.
But in the beginnings of cellular systems, each country developed its own system, which was an undesirable situation for the following reasons:
• The equipment was limited to operate only within the boundaries of each country.
• The market for each mobile equipment was limited.
In order to overcome these problems, the Conference of European Posts and Telecommunications (CEPT) formed, in 1982, the Groupe Spécial Mobile (GSM) in order to develop a pan-European mobile cellular radio system (the GSM acronym became later the acronym for Global System for Mobile communications). The standardized system had to meet certain criteria:
• Spectrum efficiency
• International roaming
• Low mobile and base stations costs
• Good subjective voice quality
• Compatibility with other systems such as ISDN , PSTN , PSPDN etc.
• Ability to support new services
GSM system is based on digital technology which has many advantages over analog technology. It also provides the technology as ROAMING, SMS
TELETEX , Fax mail.