Wirelessly posted (Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_1 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5F136 Safari/525.20)
I left Verizon for the original iPhone 16 months ago. No problems with AT&T except inside the building at work. No signal, though Sprint and Verizon devices work fine. Still not sure if the inability to receive calls at work on my cell is a good thing or a bad thing....
But everywhere else, it seems to be fine lately. Some trouble in NYC about 2 months ago, but hopefully 2.1 and ATT have dealt with that (haven't been back to NYC since).