It’s not all bad news for Yahoo (NSDQ: YHOO) these days. T-Mobile USA has picked the company’s OneSearch platform for its default search engine on mobile phones, InfoWorld reports. The carrier will be placing a OneSearch button on phones under a deal expected to be announced at the Open Mobile Summit in San Francisco later this week. It’s a notable win for Yahoo, particularly considering that T-Mobile just released the first Google-branded phone, the G1, last month. Yahoo didn’t say whether the OneSearch button would get any play on that device. Marco Boerries, EVP and head of Yahoo’s Connected Life Division, told InfoWorld that Yahoo let Google take away most of its market share in PC search and that it’s working diligently to make sure the same thing doesn’t happen in mobile. Yahoo now has deals with 26 mobile operators around the world, which count 850 million subscribers among them total. T-Mobile dropped Google (NSDQ: GOOG) search for Yahoo in markets in Northern and Central Europe last March.