Considering that all iPhone 5S variants are at least $50, if not $100 more on an ATT contract vs. other providers it does beg the question whether ATT is purposefully pricing Apple out, or is ATT so big that people will pay whatever for the iPhone just to stay on ATT's network?
iPhone 5S 16GB $199 at ATT with 2-year contract
$149 at Sprint
$99 at Verizon
$0 at regional carrier