What is "GSM"?

What is "GSM"?
GSM is a TDMA based wireless network
technology developed in Europe that is used
throughout most of the world. GSM phones make
use of a SIM card to identify the user's account.
The use of the SIM card allows GSM network
users to quickly move their phone number from
one GSM phone to another by simply moving the
SIM card. Currently GSM networks operate on the
850MHz, 900MHz, 1800MHz, and 1900MHz
frequency bands. Devices that support all four
bands are called quad-band, with those that
support 3 or 2 bands called tri-band and dual-
band, respectively. In the United States, Cingular
operates on the 850 and 1900MHz bands, while
T-Mobile operates only on the 1900MHz band.
Also known as: "Global System for Mobile
Communications", "Groupe Special Mobile"