Looks like it's hit a lot of Phoenix already, according to the map. Interesting... Great news for iPhone users on AT&T that want to break free from tiered data plans.
I was actually in the process of switching and presently have a vzw iPhone 4s... this is great because I'm planning to dig out some of my old ATT androids and I'd much rather have 3G than EDGE. I'll be trying my Nexus One and Atrix on T-Mobile