I don't think you will see an AT&T 3G version as long as Apple and AT&T are married. Google's obviously going for Apple with the Nexus One, making it available for just T-Mobile and Verizon later in the year. AT&T doesn't even have one Android phone, and there's a reason for that.
here's my take on it: Google didn't/doesn't have to make it specifically for AT&T. They can develop on that includes the 3G band that's supported by AT&T, but sell it only unlocked (this can also be used in Canada with Telus and Rogers (largest GSM carrier in Canada)). Google doesn't need to have it subsidized by AT&T. If they made it unlocked, it would pretty much be in direct competition with IPhone as AT&T is the largest GSM carrier in the US.
AT&T just announced at their developer confrence they will be getting an Android powered phone from HTC, Dell and Motorola in 2010 along with 2 WebOS based phones from Palm.
As stated above, AT&T will be getting some Android devices in the first half of this year. Even though not important, 2 WEBOS phones too. I hope this mean less exclusivity and more choices for us in the coming future.
