We've met the Pantech C810 just recently but it looks like it's already available. Amazon.com lists it as an AT&T device already.
While Amazon.com isn't giving too much information it's clear that Pantech's latest Windows Mobile device features Windows Mobile 6 Standard (so it's a Smartphone without touch screen) and that the C810 features UMTS (and most likely HSDPA). It's not yet clear if and which GSM bands are supported nor it's clear which UMTS bands are supported but anyway, the idea of the dual-slider design is quite nice:

It's now available for US$ 179.99, when purchased with a new AT&T service plan, and if you are going to buy it, please let us know how you like it.

Cheers ~ Arne