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Another less common GSM version is GSM-450 (450 MHz), sometimes also called GSM-400. It uses the same frequency as and can co-exist with old analog NMT systems. NMT is a first generation (1G) mobile phone system which was in some widespread usage in Europe and other areas. Widespread is of course a relative term since the boom of mobile phones started later with GSM.
Note, however, that GSM-1800 is known as DCS (Digital Cellular System) and it is commonly used in PCN-networks (Personal Communications Network). The term 'DCS' has long been abandoned by ETSI/3GPP. Also, GSM-1900 is known as PCS1900 (Personal Communications Service). All the different systems fall into the general category called GSM. PCS-1900 standards have been integrated and harmonized with that set of GSM/DCS Specifications, resulting in a specification for GSM/DCS/PCS based on the Release 98 Series of GSM Specifications.
In some countries the GSM-900 band has been extended to cover a larger frequency range. The extended GSM, E-GSM, uses frequency range 880 - 915 MHz (uplink) and 925 - 960 MHz (downlink), adding 50 traffic channels to the original GSM-900 band. The GSM specifications also describe railways GSM, R-GSM, which uses frequency range 876 - 915 MHz (uplink) and 921 - 960 MHz (downlink). All these specifications are known as GSM-900.
In Europe and other areas outside North America the GSM system initially used a frequency of 900 MHz, shortly afterwards the PCN network used the 1800 MHz frequency, nowadays the PCN networks are considered part of the GSM system and many phones are dual-band operating on 900/1800 MHz or tri-band adding the 1900 MHz frequency. There are even a few quad-band phones, which add GSM-850 support, allowing them to work on almost every GSM network built to date (for them to operate on every GSM network would require GSM-450 support, too).
Nowadays most phones support multiple frequencies used in different countries. These are typically referred to as dual-band or triband phones. Dual band phones can cover GSM networks in pairs such as 900 and 1800 MHz frequencies (good operation in Europe) or 900 and 1900 (Europe and America). European triband phones (and the ones offered by T-Mobile USA) typically cover the 900, 1800 and 1900 bands giving good coverage in Europe and allowing use in North America as well. American triband phones (used by Cingular Wireless and AT&T Wireless) cover the 850, 1800, and 1900 bands giving good coverage in North America but limited coverage in Europe.
Countries requiring phones which cover the 1900 MHz frequency:
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