In my honest opinion, I would wait and see what happens this summer. Verizon is also moving into limited Data plans. Verizon will most likely offer better data plans than AT&T. It was Verizon who started 69.99 voice talk unlimited and AT&T matched it about 24 hours later.
Verizon will most likely offer better rate plans than AT&T. That leaves you either switch to verizon or wait until AT&T to match that plan.
Verizon is also explained that they are considering family data plan for the smart phones with these new pricing structure. I would highly recommend for you to wait and see with iPhone 5 or 4S or 4+ or w/e they want to call it.