GSM er en 2G standard
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https://en.wikipedia.org/wiki/2G2G Technologies
2G technologies can be divided into time division multiple access (TDMA)-based and code division multiple access (CDMA)-based standards depending on the type of multiplexing used. The main 2G standards are:
GSM (TDMA-based), originally from Europe but used in most of the world outside North America. Today accounts for over 80% of all subscribers around the world. Over 60 GSM operators are also using CDMA2000 in the 450 MHz frequency band (CDMA450).[2]
IS-95 a.k.a. cdmaOne (CDMA-based, commonly referred as simply CDMA in the US), used in the Americas and parts of Asia, accounts for about 17% of all subscribers globally. Over a dozen CDMA operators have migrated to GSM including operators in Mexico, India, and Australia.
PDC also known as JDC (Japanese Digital Cellular) (TDMA-based), used exclusively in Japan
iDEN (TDMA-based), proprietary network used by Nextel in the United States and Telus Mobility in Canada
IS-136 a.k.a. Digital AMPS or D-AMPS (TDMA-based, commonly referred as simply 'TDMA' in the US), was once prevalent in the Americas, but most have migrated to GSM.
2G services are frequently referred as Personal Communications Service, or PCS, in the United States.