Hmmmmn! Interesting. Yes, AT&T does have their own network, which I was once a subscriber to. If they have it set up to deal with the cable connection, they are home free. And I doubt if it would take much to make their network compatible. (I was previously a dialup subscriber to worldnet.att.net)
This could be another strategy; get the other cable companies to hook up with AT&T's network. AT&T was in the process of getting out of cable, but were not planning to get out of the internet business as far as I know. A little different picture than I had first thought, based on what I've read here. In essence, delete @home, replace with worldnet.