Verizon Communications Inc. is adding a package that includes unlimited data, marking a reversal of strategy in order to compete in slowing a mobile market.

Verizon will charge $80 a month for a single user, $10 higher than the plan offered by T-Mobile US, which ushered in the industry's move to unlimited data last year. A plan with four phones will cost $180 through Verizon.

Verizon is trying to differentiate itself by letting customers watch high-definition video with the unlimited plan, while competitors typically run streaming video at DVD-level quality. However, T-Mobile said that starting on Friday, the company's unlimited plan would include high-definition video streaming. It also announced a new promotion of two lines for $100.

Of course, like all so-called unlimited plans, Verizon's is not really unlimited. If customers use more than 22 gigabytes of data in a month, their speeds may be slowed if the network is busy.

Verizon has been refusing to offer unlimited data plans for fear of obliterating the bottom line, choosing instead to focus on network quality for the highest-paying customers. But after another quarter of slowing subscriber growth, and with a new head of wireless and chief financial officer in the fold, the phone giant is going on the offensive.

As part of the new promotion, Verizon is also offering free iPhones to new customers with qualifying trade-ins. The company used free iPhone promotions for a few weeks during the holiday season to match similar offers from rivals.