<tangent alert>
How can we actually compare coverage from one carrier to another once roaming is taken into consideration? I use Sprint and very frequently stray from the defined coverage areas on their map. Most of the time my phone doesn't indicate that I'm roaming so I'm a little confused. I haven't had a cell phone plan in years that charged for roaming service so I honestly don't care who's network I'm on as long as my phone works.
I can only go by my experience. Can't tell you number of times I have been places and I have no problem with my Verizon phone and the guys with iPhones are cursing. My iPhone carrying friends are constantly harping about the lousy service, not just 3G, but 2G as well. <shrug> For those who stick to major metro areas, not as big a problem. OTOH, don't even try to use an ATT phone at a Denver Broncos game, so even then, their system is easily overwhelmed.
Being married to someone who was in the infrastructure business at the time, ATT's system issues are the result of some historical poor business decisions and the various mergers and such that occurred a few years back. The bottom line is that ATT basically stopped upgrading and building their system out at a critical juncture and have never caught up.