Verizon Wireless and AT&T, the nation's two largest cellular service providers, on Tuesday introduced flat-rate voice calling plans for their mobile customers.

Verizon's Nationwide Unlimited Anytime Minute plans will give Verizon Wireless customers, who pay $100 for monthly access, the freedom to make calls anytime to anyone in the United States at a flat rate.

AT&T said its plan is available to new and existing wireless subscribers for $99.99 a month for unlimited U.S. calling on all devices with no domestic roaming or long distance charges. It can be combined with any current wireless data plan.

Verizon also is offering BroadbandAccess plans with two options: 50 MB for $40 monthly access and 5 GB for $60 monthly access. BroadbandAccess is intended for Internet browsing, e-mail, and downloading files. The service typically delivers download speeds of between 600 Kbps and 1.4 Mbps and upload speeds of 500 to 800 Kbps, according to the company.

"The $39.99 plan is perfect for the occasional or light data user, while the $59.99 plan meets the needs of the majority of heavy data users. The plans are easy to understand and give customers the technology they need to manage their lives -- both business and personal," said Mike Lanman, Verizon Wireless' CMO, in a statement.

Last year, Verizon disclosed plans to roll out its fourth-generation mobile broadband network using a technology called Long Term Evolution, while also adopting a common access platform with Vodafone to provide services worldwide based on the technology.

The carrier is also expected to open up its nationwide network this year to outside mobile devices, software, and applications. It has set up a $20 million testing lab where mobile devices will be tested and approved, and will publish technical standards that software developers can use to design products that will interface with its network.