It looks like AT&T is going to launch the new UTStarcom Knick GTX75, a Sidekick-like smartphone.
The UTStarcom Knick GTX75 supports tri-band UMTS and quad-band GSM networks. It has a large color display, 1.3 Megapixel camera, a slide-out QWERTY keyvoard, 35MB memory and a microSD card slot. Not sure about the availability and pricing.
Update: The phone is officially known as AT&T Quickfire and will be available soon.