Our friends at TmoNews got their hands on a very interesting document that foretells how current T-Mobile service plans will be affected if the goes through. Though we've always known that AT&T's will honor T-Mobile's contracts through the end of their life, this employee FAQ says that customers can keep their plans "as long as they want to, even when their term ends and the service continues on a month-to-month basis."
Exactly what that means remains to be seen. In previous carrier mergers, customers were allowed to keep contracts until they bought a new handset or changed the terms of their service plan. And even then, carriers tend to do everything they can to influence contract switching, including telling grandfathered customers that their old device is no longer supported.
Granted, "as long as they want to" does imply a certain permanence, but we just don't trust AT&T on this one. It is in AT&T's interest, after all, to keep former T-Mobile customers hooked with a new contract, so we wouldn't be surprised if the carrier added a exception for new device purchases. On the other hand, perhaps AT&T is trying to curry favor for a merger that isn't exactly winning over the general population. If that's the case, and the carrier make good on this promise, then we'll gladly give AT&T credit. But in the meantime, we're taking it at face value.