I am heavily leaning towards AT&T because we get nice discounts from where I work. I talked to a someone on the AT&T site via live chat, and tried to get my questions answered but they were worthless. Seems to me the Siemens S46 is the best of all worlds.
Not necessarily a bad approach, but I did take the opposite. I decided which phone I wanted, and that determined my carrier. I suppose lack of coverage or excessive cost might have altered my choice, but more likely would have just made me put off getting a cell phone for another few years.
The phone is a Handspring VisorPhone - I already used a Visor, and I'll be damned if I'm going to manage more than one address book. The only other option would be a Treo (Warning: my brother in law tells me that they took the ability to search your address book by company out of the Treos!) or another integrated cell phone and PDA. It's a GSM phone, and I haven't had many coverage problems. Of course, so far I've taken the phone with me only to places I checked on the coverage map before buying or to Washington, DC.