Company the size of AT&T working in highly regulated areas, everything's a subsidiary for various accounting and legal reasons.
AT&T Mobile and AT&T UVerse are two different companies. They probably have different operating entities for different states, even. But they roll everything up into a single brand for ease of sales and marketing.
True, though it's interesting that you can purchase UVerse at an AT&T Mobility store. (I have a friend who's an AT&T store manager) While it has the appearance of being one company, I guess it's the rough equivalent of an "affiliate" sale.
AT&T Mobile and AT&T UVerse are two different companies. They probably have different operating entities for different states, even. But they roll everything up into a single brand for ease of sales and marketing.