The LG Quantum is one of the initial Windows Phone 7 devices on AT&T. It offers a 1 GHz processor, 3.5-inch display, and a 5.0-megapixel camera. There are a few minor quirks that bugged me, but the decent battery life makes up for it. It's available now for $199.99. Part 1 of 2.
For more, check out LG Quantum Review Pt. 2