A G is a generation. Within each of those generations there are various competingh standards, and various "half step" improvements. There is also a lot of marketing spin. 1G = analog Examples include NMT, AMPS, TACS, etc 2G = digital, voice Examples include GSM, D-AMPS, PDC Some people claim IS-95 original cdma was 3G: I'd say that as a sophisticated 2G 2.5G added data (GPRS) 2.75G faster data (EDGE) 3G = digital, supported data, but still circuit switched WCDMA, EvDO 3.5G faster data, added packet data onto CS architecture (HSPA) The USA and few ither places had a rival technology ("CDMA"). That was marketed as 3G when it was launched, but initially was probably closer to 2.5G and then upgraded to 3G with the EvD) upgraded. 4G = wireless broadband OFDMA, flat architecture, true packet switched Most people say this is LTE & WiMAX, though some people are waiting for an upgrade to LTE-A (based on a rather silly data rate definition).
2G (or 2-G) is short for second-generation wireless telephone technology.It is very slow and it's data connection is denoted by Edge (E)

3G, short form of third generation, is the third generation of mobile telecommunications technology.It's data speed is faster than 2g.(most commonly used till date)

4G, short for fourth generation, is the fourth generation of mobile telecommunications technology, succeeding 3G and preceding 5G.It supports LTE Data that is faster internet speed.