NEW YORK (Dow Jones) - Sprint Corp. (FON ) launched a pay email service with Yahoo Inc. (YHOO) for its mobile phone customers, as the companies look to tap into the rapidly growing wireless data-service market.

Starting Wednesday, Sprint users with select handsets will be able to download a program that greatly speeds up the delivery of Yahoo emails through a more user-friendly interface. It will also allow the storage of emails onto the phone, so users won't have to constantly go online to review old messages. Both Sprint and Yahoo are banking that consumers will pay the additional $2.99 a month for the new features.

The move by Sprint, which is based in Overland Park, Kan., to offer a premium version of an already-free service is consistent with industry comments regarding the explosive growth of the wireless data business. During an investor conference Tuesday, Verizon Communications (VZ) Chief Financial Officer Doreen Toben touted the market opportunities for Verizon's high-speed wireless data network.

"Once again, this adds another brick to the building that people keep discussing that's rising around the world of voice," John Styers, director of communication services at Sprint, said about data services.

While all the attention is focused on streaming video and music and unique ringtones, there is also interest in the enhancement of basic services such as messaging.

"It's less sexy, but highly useful," Styers said, adding he believes it will be broadly adopted.

For Yahoo, of Sunnyvale , Calif., this allows the Web portal to expand its presence beyond the computer and into the cellphone. While its email service is available to all U.S. carriers for free, the company is able to better cement its brand with a downloadable interface that resembles the version seen on the computer.

"It fits into the broader strategy of expanding ( Yahoo's ) relationship on the desktop to the mobile phone," said Thad White, director of mobile products at Yahoo .

Yahoo will continue to offer the free service to Sprint customers.

Yahoo and Sprint will share part of the revenue from the fee, but both companies declined to break down the numbers.

While the email feature is Yahoo's most popular, it isn't the first premium service offered. The company has a premium messaging and photo service available, and White said to expect the company to continue exploring other possibilities to offer a pay service.

"We're constantly looking at ways to deepen our relationship," he said.

The companies' research indicated there was demand for a pay email service. Styers said they are targeting customers who find email to be extremely important, but don't want to be wed to one of Research In Motion Ltd.'s (RIMM) Blackberrys.

-By Roger Cheng, Dow Jones Newswires; 201-938-2020; roger.cheng@dowjones.com Dow Jones Newswires 06-08-05 0029ET Copyright (C) 2005 Dow Jones & Company, Inc. All Rights Reserved.