I don't think it's very realistic to consider them doing that. The backlash would be immense, and there's no reason to do it in the first place. All they have

I don't think it's very realistic to consider them doing that. The backlash would be immense, and there's no reason to do it in the first place. All they have to do is work with existing ad networks. Then, when the user hits a page (the page already has an ad on it) and the ad network determines that the user is an AT&T subscriber, the ad is targeted using that data, and AT&T gets a cut.