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A digital cellular telephone technology that is based on time-division multiple access; it operates on the 900-megahertz and 1.8-gigahertz bands in Europe, where it is the predominant cellular system, and on the 1.9-gigahertz band in the United States. Derived from global system for mobile communications.



(Global System for Mobile Communications) A digital cellular phone technology based on TDMA that started in Europe and migrated to other continents. GSM defines the entire cellular system, not just the TDMA air interface. In the early 1990s, GSM enabled roaming across European nations for the first time, and today, more than 1.5 billion GSM customers worldwide can phone each other via roaming agreements between the carriers. AT&T and T-Mobile offer GSM service in the U.S., while Rogers Wireless uses GSM in Canada.

GSM operates in several frequency bands, including 900 MHz and 1.8 GHz in Europe and 850 MHz and 1.9 GHz in the U.S. and Canada. GSM's TDMA technology is based on a circuit-switched system that divides each 200 kHz channel into eight 25 kHz time slots.

The SIM Card
GSM phones use a Subscriber Identity Module (SIM) smart card that contains user account information. Any GSM phone becomes immediately programmed after plugging in the SIM card, thus allowing GSM phones to be easily rented or borrowed. SIM cards can also be programmed to display custom menus for personalized services.

Text and Data
GSM includes the short messaging service (SMS) that enables users to send 160-character text messages to each other. It natively supports very slow data transfer at 9.6 Kbps; however, carriers have added higher data rate technologies. See GPRS, WCDMA, EDGE, HSCSD, GSM Association, GSA, TDMA, CDMA and PCS.

Vive la Cellphone!

When GSM phones were introduced, they were reported to produce a deafening sound for hearing aid wearers and to interfere with electronic devices such as pacemakers. Swedish hospitals banned them. An Australian newspaper claimed a motorist set off his airbag with one, and most curious, in Paris, they were said to occasionally reset taxi meters to zero.

The SIM Card
The back of a GSM phone opens, and the tiny SIM card is inserted, as in this example from Europe's Amena cellphone service. The bottom view is the card outside the socket showing contact points.

Evolution of 3G Technologies
This chart shows the evolution of carrier technologies throughout the world as they move from standard cellphone services to high-speed data capabilities.
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