AT&T will let you keep your existing plan. If you change your plan, though, you'll have to deal with AT&T's options and won't be able to revert to your old plan.
This may or may not apply upon contract renewal (I've seen it happen both ways, where you have to choose a new plan or are allowed to stick with the old one).
This may or may not apply upon contract renewal (I've seen it happen both ways, where you have to choose a new plan or are allowed to stick with the old one).