Yahoo’s (NSDQ: YHOO) oneSearch has, as expected, become the chosen web search service for AT&T’s (NYSE: T) mobile portal - actually Yahoo’s first US carrier for the service. We knew, when the pair unveiled an expanded strategic partnership in January, that Yahoo would power AT&T search; specifically, oneSearch will also return results from the ringtones, wallpaper, games etc available in AT&T’s own MEdia Mall, and Yahoo will facilitate search advertising on the deck.

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Introduced in March 2007, oneSearch differs from offerings like Google’s (NSDQ: GOOG) by making search more relevant to the mobile experience - there’s a greater emphasis on content like movie times, weather and picture search, and fewer links to page through. Originally introduced as part of the rather slow Yahoo Go app, there is now also a web version of oneSearch, carried by T-Mobile UK and America Movil’s south American territories amongst 29 networks. Other parts of this alliance were a Yahoo-powered web homepage with ad rev share, with Yellowpages.com feeding Yahoo search for business listings. Release.

Update: AP reports that Yahoo’s oneSearch replaces Motricity on AT&T’s MEdia Net cell phone portal, which gained the business with AT&T through its acquisition of InfoSpace’s (NSDQ: INSP) mobile group.