Go to the Sonic prequalifation page ( http://sonic.net/solutions/home/internet/
) and use the "Check using my home address" link and put in the physical address. That should tell you whether it's within an AT&T service area.
If you're looking for Fusion, order service, Sonic will have AT&T install the appropriate line to the home. If you want regular wholesale DSL, you'll have to order a phone service from AT&T first, then have Sonic add DSL to it.