Google may have teamed up with T-Mobile to launch the G1, but I heard from someone close to the matter that Yahoo! will soon be the default mobile search engine on T-Mobile USA’s mobile web portal. All phones launching from November 8th will have a shortcut button to Yahoo! OneSearch, except obviously Google G1 and the new Sidekick.

Yahoo! OneSearch will allow T-Mobile USA customers to search for on-portal content such as games, ringtones, news, etc but also off-portal content.

Medio is currently T-Mobile USA’s mobile search provider but I don’t know if it will still remain present on its deck, I should have more details on that soon.

Yahoo! was already T-Mobile partner for mobile search in Europe, with T-Mobile USA it will have the potential to directly reach 30 million subscribers.