Comment AT&T shot themself in the foot (Score 1) 249
Basically, verizons 3G service cdma2000, was a bolt on replacement upgrade to go from their 2G tech (cdmaOne). EDGE for AT&T was also a bolt on upgrade from their 2G tech (GPRS - a TDMA signal, not CDMA). Verizon just stopped after doing this bolt on upgrade so their entire network is considered 3G pretty much.
AT&T then decided to go with an entirely different 3G technology because it was way faster than EDGE (even though EDGE is considered a 3G tech). This new tech was HSDPA which is based on a CDMA network, not TDMA. Therefore, AT&T has to deploy entirely new towers to roll out this new 3G service so their 3G map is much smaller than Verizons. Technically EDGE is still a 3G tech though.
If AT&T still marketed EDGE as 3G and then maybe HSDPA as 3.25G or something, Verizon could not be making this claim. And technically speaking, AT&T would be on solid ground for doing so.
See the "Overview of 3G/IMT-2000 standards" chart at http://en.wikipedia.org/wiki/3G to clarify.