Ideally I'd like to wait for Helio to roll out their hardware and plans, but I can't find any press releases announcing availability dates.
I'm going to try Cingular ... I say "try" because I just ordered a Sony Ericcson w600i from Amazon on a special promotion (the phone is free with activation, and I actually get $50 back). The Cingular contract gives me a 30-day grace period to back out without a fee, if I want (have to return the phone, though).
Coincident with that, I'm going to ask T-Mobile, my current provider, to upgrade my handset for free. I like the Samsung SGH-t809. I figure it's worth a shot: I've never paid a bill late, and I've never asked for an upgrade before. Hopefully I can also get a grace period, so that I can test out both phones at once.
It's ON, bitchez!