Analog cellular phones were the first generation while digital marked the second generation.
3G is loosely defined, but generally includes high data speeds, always-on data access, and greater voice capacity.
The high data speeds are possibly the most prominent feature, and certainly the most hyped. They enable such advanced features as live, streaming video.
There are several different 3G technology standards. The most prevalent is UMTS, which is based on WCDMA (the terms WCDMA and UMTS are often used interchangeably).