I would guess that the Sprint version will be the first CDMA device that is released. So, unfortunately, there is almost no chance that you could even find a CDMA phone before then. Even if you did, you would have to get Sprint to accept it on their network, which wouldn't be likely.
Even if you wanted to get a GSM phone to use on AT&T you would be out of luck because our 3G data operates on different frequencies than most of the rest of the world. You'd be stuck with EDGE speeds
We just have to wait till the devices are officially brought to the US, which is looking like Q4 of this year.