GSM is a combined channel access system of FDMA (Frequency Division Multiple Access) and TDMA (Time Division Multiple Access) . In Bangladesh, Teletalk , Grameenphone , Banglalink , Robi and Airtel mobile operators are using GSM technology. GSM technology was introduced for mobile phones in 1991 through the GSM Consortium. GSM technology is currently the most popular mobile network in the world, used in 216 countries. Therefore, international ramming facility is more available in this technology. Due to the availability of SIM , users can change the GSM network and handset or mobile set at will. This technology provides high speed technology GPRS (General Packet Radio Service) and EDGE (Enhanced Data Rate for GSM Evolution) for mobile data transmission . Its cell coverage area has so far been limited to about 35 kilometers. The power consumption is comparatively higher which is about 2 watts on average ; Where as CDMA technology averages only 200 microwatts. Its data transfer rate is relatively low which is 56 kbps . Due to the use of Pulse technology in GSM , the use of mobiles in hospitals , airplanes, etc. is prohibited.