Discussion from ArsTechnica on the current cellular technologies and their coming evolutions as we enter the 4th generation.
In short:
There are four defined generations of cellular technology. 1G was all analog. 2G is digital, with a small provision for data networking at speeds slower than dial-up modems. 2.5G was a stopgap of 100 to 200 Kbps data networking while 3G was finalized and deployed. 3G networks needed to have a raw downstream rate of 2 Mbps or higher, but voice and data traffic are managed separately. 4G networks are ostensibly all Internet protocol with low latency to allow voice and video to work well without extra effort.