Just a bit of info on WCDMA
The problem is indeed att, but another thing you don't realize is that verizon has put alot of money into their network a couple years ago making it robust whereas att puts it in as needed. The main limitation to this inability to connect make calls etc is back haul and 3G power itself.
You might have seen recently att press releases about 2nd carriers of 3G. WCDMA technology otherwise known as 3G on ATT, is a shared power system. The more users that are on the more noise there is the less coverage there is. During the course of the day cell sites footprints will shrink due to load (known as breathing) which is part of your reason for poor coverage and data speeds. The other is lack of resources on att's back haul side. They def don't have the back haul to support many users requesting lots of data. I think the approach they have taken is reactive, not proactive, but I also think they were not expecting the sheer amount of data that iphone uses consume. Don't think that they are idly sitting by and letting their service going to crap, but it takes time to beef up their network.
Could they do a better job making it better? Oh hell yes
Im not supporting att, just trying to educate
The next time your 3G iPhone cannot make a call or send a text, try turning 3G off...just a thought