The Global Systems for Mobile Communications (GSM), is a radio-based technology that allows mobile phones to communicate. GSM is considered to be the world's most ubiquitous radio-based cellular technology, with 1.7 billion users as of March 2006. In the United States, carriers such as T-Mobile and Cingular utilize GSM technology for their cellular networks.

GSM Cell Phone Providers

USA

Cingular
T-Mobile

Other

T-Mobile
Vodafone
O2

Operational Characteristics

Network Principles

GSM is considered to be 2G and uses digital data for both signaling and voice purposes. GSM uses a time division multiple access (tdma protocol to transmit information. Aside from voice, GPRS and EDGE allow for data transmissions across a GSM network.

Radio Communication

In terms of frequencies used, GSM networks often use the 900MHz and 1800MHz bands, but carriers in the United States use 850MHz and 1900MHz bands. As a result, "dual-band" phones, which only support two of the four major bands, can only be used in certain parts of the world. More common are "tri-band" phones, which usually operate on 900/1800MHz and 1900MHz. "Quad-band" phones support all four frequencies and can be used in all parts of the world.

GSM Forensics

For phones with a SIM card, perform forensics on the cell phone before removing the SIM Card.