I got my iPhone4 earlier this year when it came out on Verizon. I was living in Milwaukee and I was suprised by the call quality. (the lack of it) In July I moved to Albuquerque, NM. My call quality improved big time! No more dropped calls, no more issues with people breaking up. My conclusion was it isn't just the phone that matters.
That said, there is definitely an issue. My wife's dumbphone worked completely fine in Milwaukee and so was my previous phone. What about the iPhone is giving people these issues? Obviously we can point at the antenna. But why would it work completely fine in some areas and not others? Milwaukee is MUCH larger than Albuquerque. Am I to believe that Verizon's network is actually better in a smaller metropolis? Or is there some other combination of things that is going on here. A quick search of android call quality shows that there are plenty of folks out there with issues on those phones too. So what gives?