AT&T does not "resell" HSI services to 3rd parties, so that connection is mute, you must be using a line share type service from that independent, like Covad use to do.
ATT does indeed resell DSL... off the top of my head to both DISH and DIRECT TV.
Been a while since I have had resold DSL as they had a tendency to go out of business or over extended themselves. --
