Looking for incentives to add new subscribers and keep existing ones for its DirecTV and U-Verse TV, AT&T has brought back unlimited mobile data. The carrier did away with the all-you-can-eat data offerings back in 2010. There are still grandfathered unlimited accounts paying $30 a month for the service, but that is expected to rise to $35 next month. At that price, it is still a sweet deal. But we digress. Today's news means that starting tomorrow, DirecTV and U-Verse customers can pay $100 a month for unlimited data from AT&T. Additional lines will cost $40 monthly, and ...