According to IntoMobile, that might not happen. At CTIA 2011, AT&T Mobility's president and CEO, Ralph de la Vega, told IntoMobile that T-Mobile will keep their pricing structure. But how will that work?
If AT&T brings T-Mobile into the fold, they will either have to change the rates of T-Mobile or AT&T customers. On the other hand, they could leave T-Mobile as a separate arm, much like Sprint does with Boost Mobile.
What he may have meant is that existing T-Mobile customers will be able to keep their rates, even after T-Mobile is absorbed into AT&T. But new customers will be subject to AT&T's existing pricing structure. It's anybody's guess at this point, but with the level of controversy this deal has generated, we doubt AT&T will want to further aggravate their customer base.