Interesting. I get very good 3G reception in NW DC and MD suburbs. The only place where it's sketchy is McLean and that whole Glebe road Chain Bridge area. But I think that has more to do with NIMBY than ATT and Apple. GSM is also pretty weak in that area.
The other day I started a phone call near Gaithersburg on 270, and held the call perfectly into downtown DC. And that's roughly a 20 mile trip. The call was crystal clear, didn't experience the strange garbling that I would get on my 2G iPhone and Blackberry.
overall I'm pretty satisfied with 3G in my area.
Georgetown and Embassy Row is where I have the most problems with 3G signal. Reception at my house in Northern Virginia is fine, only because the tower is about a 1/4 mile away (and just my luck, no need for 3G at my house because I have WiFi).
I really don't believe a replacement iPhone will solve this, but I guess anything's possible. For now, I'll just keep it on EDGE and see how this pans out. It is damn irritating not being able to just keep it on 3G full time in Washington, DC without having issues.