Here's a piece in The N.Y. Times that says SBC will take the venerable name AT&T once the acquisition is approved.
One response: Will the AT&T brand support the kinds of Internet-age services that SBC is offering and wants to offer (i.e., IPTV)? One could argue it's really a 19th-century brand.
Another response: It doesn't matter. No one knows that 3M originally stood for "Minnesota, Mining and Manufacturing." What does Google mean? What does Yahoo! mean?
I'm certainly no branding consultant, but unless there's a truly negative consumer association with SBC (little evidence there is) it doesn't matter whether the company calls itself SBC, AT&T or Howard Stern (well, maybe not Howard Stern). Of course, it will cost millions and millions to do the rebranding (think about repainting all those trucks: AT&T-Yahoo! DSL).
Ultimately, however, the perception of the consumer and the value of the brand is all about what's going on behind the brand.