I was with AT&T for years. They always had back office problems. Doing simple things was not always simple with them. When they merged with Cingular there were really two sides to Cingular, Blue (AT&T) and Orange (Cingular). The blue side continued to have issues. They kept trying to get me to switch to the Orange side, but they never offered a plan that was as good as the one I had on the Blue side.
I finally switched to Verizon, and I was amazed at what a difference it was any time I needed to call customer service. It was like dealing with a real company, that didn't have any internal problems fulfilling your request.
I purchased the phone and plan from amazon.com in a double rebate deal that ended up netting me $50. (Well, it would have had I submitted the $50 Moto rebate, but I never did.) I had some problems getting the big rebate from amazon, but a few emails with amazon customer service fixed that.
If you want GSM, so you can use your phone in GSM countries, you're probably better off going with t-mobile or cingular. If that's not an issue for you, you can just pick the best deal among the various providers without worrying about the technology.
I have to say, that I liked my older Sony Ericson t616 a lot better than the Moto phone that I have now. Verizon criples the bluetooth capabilities of the phone with their firmware, but that's defeatable to some extent, but you still won't get the bluetooth in the phone to export the right profile so you can exchange phone numbers with somebody else by bluetooth. My Sony t616 was so old, it started having some problems, so that's what made me look around for something else.
My company has discount deals for personal phone plans with all the major providers. The amazon rebate deal was only valid on plans of $39.95 a month or higher. I checked with amazon to make sure I was still eligible for the rebate if I applied my corporate discount to the $39.95 a month plan, and they told me I was, and the fact that they told me that was accessible to amazon CSRs later when I had the rebate problem. I think the rebate problem was unrelated to the discount, but it was good knowing that it wasn't like the airlines where one agent tells you one thing and another agent denies it and has no idea what the first agent told you. I was impressed that they actually kept a record of what other amazon CSRs told me at any point. I think that also helped get the rebate in the end, because they had a record of my problems with that and in the end they just instructed their rebate provider to cut the check and send it to me.
Even with the corporate discount on equipment, the cheapest place to buy the phone for me was on amazon. Once activated, I followed the corporate instructions to get the discount applied to the account.
-David