The companies said the premium service, which costs $2.99 a month, is faster and easier to access and sports a PC-like interface. An optional instant-messaging feature is available at standard text-messaging rates.
The new service builds on the existing partnership between Yahoo and Sprint, under which PCS Vision customers can send and receive e-mails, files and photos from their mobile phones.
Although Yahoo Mail for Mobile is already a free service, the two companies are hoping to entice customers with the improved features.
"Sprint recognizes the increasing desire of customers to have a more robust messaging experience on their handset," John Styers, director of data communications services at Sprint, said in a statement.
The service initially is available only to customers with Sprint PCS Multimedia MM A700 phones by Samsung, the MM 7400 and 5600 versions by Sanyo and Sprint PCS Vision Smart Device Treo 600 and 650 from PalmOne.
Meanwhile, Yahoo and Google have been, as each seeks to grab a larger share of that market. Both now offer search services to cell phone carriers.