Remember when AT&T killed off its unlimited data plan, unless you were grandfathered in? The AP reports that the carrier is quietly backtracking to allow customers who previously had unlimited data—but switched to tiered pricing—to return to all-you-can-eat.
If true, the move seems like a clear response to Verizon's $US30 unlimited data plan for the iPhone. Although it's worth noting that the AP cites only one instance of the rollback, and that AT&T won't confirm that this is company-wide policy. though. Which means that it could be a case-by-case basis, at least until Verizon's unlimited plan gives way to its own tiered system.
Still, couldn't hurt to check if you happen to be one of those cases.