The deal, announced by the two companies at thein Barcelona, demonstrates Yahoo's momentum in mobile services worldwide despite the uncertainties raised by Microsoft's takeover bid.
T-Mobile had been Yahoo rival Google's breakthrough mobile partner.
Beyond the nearly 90 million phone customers that Yahoo stands to reach through T-Mobile, the deal, signed Wednesday, shows
Marco Boerries, the senior vice president in charge of Yahoo's mobile phone push, said the exclusive deal brings the number of subscribers covered by partnerships Yahoo has struck with mobile carriers over the past year to more than half a billion potential phone customers.
"We are now passing 600 million," Boerries said.
During 2008, Yahoo plans to focus on joint marketing efforts with its carrier partners to convert these potential customers into regular users of Yahoo Internet services on their phones.
Financial terms were not disclosed.
The agreement takes effect at the end of March, when the previous T-Mobile deal withexpires, T-Mobile and Yahoo said in a statement.