3G is the third generation of mobile phone standards and technology, after 2G. It is based on the International Telecommunication Union (ITU) family of standards under the International Mobile Telecommunications programme, "IMT-2000". 3G technologies enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. Services include wide-area wireless voice telephony and broadband wireless data, all in a mobile environment. Typically, they provide service at 5-10 Mb per second.
Unlike IEEE 802.11 networks, 3G networks are wide area cellular telephone networks which evolved to incorporate high-speed internet access and video telephony. IEEE 802.11 (common home Wi-Fi) networks are short range, high-bandwidth networks primarily developed for data.
In December 2005, 100 3G networks were operating in 40 countries, according to the Global mobile Suppliers Association. In Asia, Europe, Canada and the USA, telecommunication companies use W-CDMA technology with the support of around 100 terminal designs to operate 3G mobile networks.
UMTS / HSDPA / HSUPA devices operate in the UMTS frequency bands 800/850/1900/2100 or 850/1700/1900/2100 MHz:
2100 (downlink) / 1900 (uplink) for Europe and Asia (usually referred simply as W-CDMA 2100)
1900 / 850 (independently, for both the uplink and downlink) for America (e.g. AT&T Mobility)
2100 (downlink) / 1700 (uplink) for America (e.g. T-Mobile)
800 for Japan, Australia
Note that being UMTS / HSDPA / HSUPA quad band doesn't mean that phone is a GSM / GPRS / EDGE quad band. An HSUPA quad band could not be a GSM at all. However nearly all HSUPA quad band are EDGE quad band too.
Five and Six band phones (800/850/900/1700/1900/2100) are possible but none have been announced.