Image via WikipediaQ: What can you tell me about 3G, UMTS, W-CDMA, HSPA, GSM, CDMA, LTE, and all that?

A: Oh, boy, that's a long story.

First, 3G is a generic term used by marketing. ITU, the standards body, calls it IMT-2000. That is the FORMAL definition of "3G".

Within IMT-2000 there are 2 "families", 3GPP, and 3GPP2. 3GPP means "3rd Generation Partnership Project". The two families are working on different but competing standards.

Within the 3GPP camp, the overall term is UMTS, or "Universal Mobile Telecommunication System" but it is sometimes called 3GSM, as it is derived from GSM (a 2G standard). However UMTS is the official term used by 3GPP to describe the RADIO technology. The overall tech scheme is W-CDMA, or wideband code division multiple access. It is a way to push multiple pieces of data simultaneously over multiple frequencies (sometimes called "spread spectrum"). 


Within UMTS, there are various technologies and "releases" introduced over time to improve the standard. HSPA, or High Speed Packet Access. Within HSPA, there are two versions, Uplink, and Downlink. So you get HSPUA and HSPDA. Later revision updated that to HSPA+, and even within HSPA+ there are 3 versions, 14, 21, and 42 (refering to downlink speeds).

Within the 3GPP2 family, there is CDMA2000 and its variations / releases, which would be 1xRT, EV-DO (and its variations), and later, SV-DO.

Any way, onto 4G.  ITU approved the next generation, 4G, standard as IMT-Advanced.

LTE (Long Term Evolution) is a 3GPP standard trying to push beyond their UMTS (3G technology) by adopting some newer technology to make it "4G". It is not fully compliant with IMT-Advanced. LTE-Advanced, the next version, will be fully compliant.

WiMAX is a completely different technology. It stands for "Worldwide International standard for Microwave Access", and is based on Microwave transceivers. It can be used as broadband access in a cellphone. It is not fully compliant with IMT-Advanced as well, but next version should be.

Recently ITU gave in to phone carriers and relaxed the definition of "4G", allowing even 3G-derived technology such as HSPA+ to be called "4G" as long as it delivers significant speed increase over normal 3G data transmission rates. 

Hope that clears things up somewhat.