As usual, I agonized over this particular consumer decision for several months. I have an old and busted Sony Ericsson T616 that's almost 3 years old at this point. I didn't feel like switching carriers so chose among the Cingular phones available.
I really liked the Nokia E62 but turns out because Cingular classifies it as a PDA, you can only get the "PDA Connect" unlimited data plan for $45/month which is kind of ridiculous. I also was interested in the Sony Ericsson W810i and maybe the Motorola SLVR L7 but they both are just regular non-smart phones.
So I went and figured out which phones of theirs qualify for the "Smartphone Connect" unlimited data plan for $20/month. I ended up with the HTC Star Trek, which Cingular rebadges as the Cingular 3125. It's a thin Razr-style clamshell phone that runs Windows Mobile 5 Smartphone Edition, so a lot more functionality.
I went thru Letstalk.com to get the best discounts and whatnot, but with converting from AT&T to Cingular some of the rebates have to be done as mail-in rather than instant if you start out already having a Cingular phone. It was $169 and a $50 rebate will bring it down to $119. I have the basic Cingular Nation 450 w/ Rollover plan for $40/month and added the Smartphone Connect unlimited data plan for another $20/month so I'm still not paying too much.
Report to follow once the phone gets here on Wednesday...