I use a Verizon BlackBerry, and as much as I would love to move to the iPhone, I don't think I can put up with more than 1-2% dropped calls. I use the phone a lot for business.
In the past 2 years with Verizon, my Verizon BB may have dropped 5 calls out of thousands made and received. Not a bad track record.
My question to other New York City area iPhone users is: what's your estimated percentage of dropped calls with AT&T?