ATT is making its shared-data family plans a lot more appealing starting tomorrow. The carrier is slashing the price of Mobile Share Value plans that come with 10GB or more of data; The carriers Mobile Share plans have long operated the same way: you purchase a bucket of data (alongside unlimited talk and text) to share with everyone on your account, and then pay an additional fee per month to add devices. ATT recently overhauled its pricing structure to give discounts to off-contract customers and those using the Next early upgrade plan, and now its making a tweak to make large data plans less expensive.