AT&T is reportedly offering some customers unlimited iPhone data plans in an attempt to keep them from defecting to rival carrier Verizon, where Apple's handset will launch on Feb. 10.

According to The Associated Press, AT&T is employing an "unadvertised loophole" in an effort to retain some subscribers who contact customer service. The carrier is said to be quietly offering the option to customers who had a previous version of the iPhone prior to June 2010, when the carrier offered an unlimited data plan for $30.

Though AT&T wouldn't confirm the option, the report cited a resident of Brentwood, N.Y., who said he and a friend were switched back to an unlimited plan after they contacted the carrier's customer service and threatened to swtich. Both subscribers are iPhone 4 users who owned a previous version of the iPhone with an unlimited plan.

AT&T introduced tiered data plans with lower pricing in June 2010. New customers can receive 2GB of data for $25 per month, or 200MB for $15 per month.

Customers who signed a contract for $30-per-month unlimited 3G data prior to last June can keep the plan until their two-year contract expires. Those customers have been able to keep their unlimited plan when upgrading, but the ability to switch back to unlimited, after choosing tiered, has apparently been secret.

Claims that AT&T is offering some customers an unlimited option come as the iPhone 4 is just weeks away from going on sale for Verizon customers. This week, the carrier revealed it would offer unlimited data for iPhone customers for $30 per month.

Verizon Chief Operating Officer Lowell McAdam said Verizon hopes its unlimited offering will help the carrier attract more customers away from AT&T. He said canceling the company's unlimited plan would create a barrier for customers who might otherwise switch.

"I'm not going to shoot myself in the foot," McAdam said on Tuesday.

But Verizon's unlimited data plan will only be available for a limited time, as the carrier has indicated it intends to move to a tiered structure with caps on monthly data use, much like AT&T did last June. Verizon has not indicated when it will adopt tiered plans, but the company has expressed interest in making the change in the near future.