here is my experiance
I voted Tmobile for my own personal needs.
I have had all service providers in the past 4 years over a range of areas.
I pretty much found that on either coasts, tmobile, verizon and ATT/Cingular are about the same, all have hit or misses but about avg.
In the middle-ish of the country however, it would say it is a no contest for verizon.
Sprint/nextel i have seen intemittant just about everywhere.
Tmobile has the best rates in the USA, and overall, i have had the best customer service with them. In fact, I love tmobile. I only wish they had got the iphone USA, becuase I would have LOVED not to switch.
ATT/Cingular: i really have no problem with their cellular service, although I have found their customer service to be the 100% worst I have dealt with ever. It was striking how bad every experiance I had with them was. cellular Service wise, they are fine.
Really, I dont know what everyone is really complaining about with ATT, my iphone is working 95% exactly as described, I am so happy.
plus, SOO many people are switching to ATT, soon it will be the absolute largest network, means free calls for me.
Apple probably went with whomever would give the cheapest data deals. after all, iphone would be an ipod without the data.
A