• are in higher frequency band (2 GHz and beyond) with larger bandwidth (around 5 MHZ) than 2G
• will provide higher speeds up to 2 Mbps in a fixed or stationary wireless environment and at 384 Kbps in a mobile environment.
• hope to converge towards one international standard for 3G. This is unlikely to be fulfilled soon because of vendors' self interests, existing infrastructure dependencies and migration steps like 2.5G GSM/GPRS, 1xRTT CDMA, Edge, etc. before a common UMTS network becomes pervasive 

Topics Related to 3G Evolution: 

EDGE Enhanced Data rates for GSM Evolution
Enhanced Data rates for Global Evolution (EDGE) is a radio based high-speed mobile data standard. It allows data transmission speeds of 384 kbps to be achieved when all eight timeslots are used..

EDGE was initially developed (by Ericsson) for mobile network operators who fail to win Universal Mobile Telephone System (UMTS) spectrum. EDGE gives GSM operators the opportunity to offer data services at speeds that are near to those available on UMTS networks.

EDGE can also provide an evolutionary migration path from GPRS to UMTS by implementing now the changes in modulation that will be necessary for implementing UMTS later. The idea behind EDGE is to get higher data rates on the current 200 kHz GSM radio carrier by changing the type of modulation used, whilst still working with current circuit (and packet) switches.

• TDMA Edge - North American version of European GSM Edge initiative - an interim step for TDMA IS-136 networks before 3G - same principles of band but on a different band, different  network infrastructure and different modulation technique
• cdma 2000 - North America's other offering in answer to Europe's 3G UMTS standard - a rather simplistic explanation. cdma2000 is a 3G technology that increases data transmission rates in CDMA systems. cdma2000 has been renamed the 1x Multi-Carrier mode (1x MC), which provides a 307 Kbps data rate in the ITU's 3G specification. The ITU 3G specification also includes a 3x Multi-Carrier mode (3xMC) at 2 Mbps as well as W-CDMA, the 3G path intended for GSM carriers in Europe and Japan to upgrade to 3G CDMA (Source - TechWeb definition)
• GPRS - General Packet Radio Service - another interim step towards 3rd Generation
• HSCSD - High Speed Circuit Switched Data - an interim step that gives 38.4 Kbps wireless speed 
• UMTS - Universal Mobile Telephone System - 3G GSM standard primarily in Europe - UMTS is the standard for delivering 3G services being developed under the auspices of ETSI. It builds on  GSM standard for increasing the speed and capacity by increasing the carrier bandwidth in a slightly different band. With Europe already committed on long term basis and North America reluctantly and grudgingly moving forward along with competitive standards. It offers the prospect of a truly global wireless standard for personal multimedia communications.
• WCDMA - Wide CDMA - See Ericsson's explanation

Evolution From 2G to 3G (2.5G)
Following scenarios are most likely:

• Current 2G GSM networks ---->Wideband CDMA (W-CDMA) for 3G
• Current TDMA networks (e.g. AT&T's TDMA network)  -----> W-CDMA
• IS-95 (Non-Wideband CDMA) ----> cdma2000