I don't think ATT-B is telling the whole story here.
I'm a MediaOne/AT&T subscriber and have been told that my .mediaone.net addresses are going away. But did AT&T even try to preserve them? Did they put up a realistic fight? There's no record, is there?
My suspicion is that they just use this as an excuse. There are many overlapping trademarks out there. Digital.com was a computer company when digital.net was a Florda ISP. Biostar.com does biological testing; biostar.net makes motherboards. Diningout.com and dining-out.com are competitors. So the other "media one", whomever they might be, could use some other domain that sounds the same. AT&T-B, I suspect, just wanted to screw the mediaone users the same way the @home users were screwed, with some kind of cockamamie notion that having peoples' mail in the attbi domain is better advertising for them than having them use the obsolete mediaone brand name.
AT&T-B is in the process of being sold to Comcast. Will the .attbi.com addresses remain, or will Comcast decide to change them again? This creates a real demand for third-party redirection services and mail services, so that users won't have to change twice!