In an interview to Brian Chen, New York Times, Ralph de la Vega (pictured), President and CEO, AT&T Mobility was asked whether AT&T is going to bring back the unlimited data accounts, following the offering of T-mobile (here) and Sprint (chart below), both with Apple's iPhone5.
The short answer was "None at this time". AT&T counts on its customer loyalty - "We’ve seen Verizon get the iPhone, we’ve seen Sprint get the iPhone and offer unlimited data plans. And now T-Mobile will get it. But while all that’s happened, our customer loyalty has improved and churn has gone down".
See "C.E.S. 2013: Ralph de la Vega of AT&T Mobility" - here.