1G = analog - (NMT, C-Nets, AMPS, TACS) are considered to be the first analog cellular systems, which started early 1980s.
2G = digital, voice - (GSM, cdmaOne, DAMPS) are the first digital cellular systems launched early 1990s.
2.5G added data (GPRS, cdma2000 1x) - (GPRS, cdma2000 1x) are the enhanced versions of 2G networks with data rates up to about 144kbit/s.
2.75G faster data (EDGE)
3G = digital, supported data, packet switched (UMTS FDD and TDD, cdma2000 1x EVDO, cdma2000 3x, TD-SCDMA, Arib WCDMA, EDGE, IMT-2000 DECT, HSPA and HSPA+)
4G = wireless broadband (LTE and WiMax)
5G = not yet defined