It won’t be cheap, but you can buy an HTC HD2 with proper bands for 3G on AT&T. It comes in the form of the unlocked Telstra HD2 T9193, which has the UMTS 850 band (one of the bands needed to get 3G on AT&T). Currently there are two listings on eBay for the T9193, both of which are around $900. See here for listing one, and here for listing two. If you decide to liquidate your savings to pick one up, come back and tell us how it works!