The Barcelona Mobile World Conference unveiled a new service brought by Yahoo, oneConnect, a “socially connected address book” combining e-mail, SMS, instant messaging and social networking and at the same time, an open service that allows other companies to join, Yahoo said on Tuesday.

Marco Boerries, executive vice president for Connected Life at Yahoo said at the congress held in Barcelona that the service will become available this spring as part of the Yahoo Go 3.0 mobile platform. OneConnect is actually an all-in-one service, designed to keep users in touch with the latest changes of their social networking contacts, by mixing social messaging and social applications for the users’ best convenience.

The service will support sites such as Facebook, MySpace, LinkedIn, Hi5 and others and will be compatible with instant messaging services like Yahoo Messenger, Google Talk, AOL Instant Messenger and MSN Messenger. OneConnect is expected to make its debut in the United States around March this year.

“The key driving force in opening up the platform is putting content into the device. No company can create these ecosystems alone. We have to be open,” said Boerries at the Mobile World Conference in Barcelona, the Associated Press reports.

Boerries also announced the collaboration with the cell phone carrier T-Mobile, that will provide its European customers access to Yahoo Mail, Yahoo Messenger, Yahoo Weather and other related services. T-Mobile dumped Google for Yahoo because Yahoo’s mobile search technology was far superior to what Google had to offer, as Hamid Akhavan, T-Mobile chief executive, said.

Yahoo is also thinking about negotiating all-inclusive tariffs for the one Connect service, especially for its European users. The large amount of data sent to and from the mobile phone could turn the service into an unattractive one, due to high costs for its customers, but Yahoo is thinking about introducing prices for unlimited amount of data, similar to the U.S. system.