Here is some interesting, albeit costly ($800+ on eBay) and limiting (AT&T and UMTS 850-band only)... It seems that the Australian version of the Touch HD uses the same band of 3G that AT&T uses partially here in the U.S., namely the UMTS 850 band...
Below is a great map of where AT&T's UMTS 850 band is being utilized... From
here