AT&T is serious about keeping its customers. The company on Wednesday introduced a new plan that will give customers unlimited calling to any mobile number.

[ad#Google Adsense 300×250 in story]According to AT&T, unlimited calling to any mobile number is available to customers with an unlimited messaging plan and a qualifying voice plan. You’ll have to check to see if your current voice plan is supported for the new feature.

The company said that existing customers with an unlimited messaging plan can activate Mobile to Any Mobile by visiting the AT&T Web site.

David Christopher, chief marketing officer, AT&T Mobility and Consumer Markets, called it “an exciting offer that will keep our customers connected to the people they want to talk to, when they want to talk to them, without the hassle of watching minutes.”

Of course, AT&T is getting set to battle Verizon for iPhone customers, so any incentive for customers may be enough to sway them in their decision.