Telefonica (NYSE: TEF) has struck a deal with Yahoo (NSDQ: YHOO) that will install the search site’s oneSearch mobile web search as the search engine of choice on the telco’s UK, Ireland and Latin America mobile web portals. That means O2 in Europe and Telefonica in the 13 countries in Latin America but the announcement did not refer to Telefonica’s native Spain. It’s a win for Yahoo over rivals like Google and other white-label mobile search providers. OneSearch formats search results for the mobile experience and includes search result categories including news, movies and images so users don’t need to wade through a single list of disparate results. It’s also available as part of Yahoo’s Go mobile app, but web availability gives Yahoo the flexibility to ink these on-portal deals without having to convince networks to place the app on handsets.

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The partnership will give both companies a share of mobile search advertising revenue. It will also bundle Flickr in to Telefonica’s portal and Yahoo Mail in to its Mail Express service, and customers can get Yahoo mail via MMS. O2’s new data tariff bolt-ons come in to effect today - 7.50 pounds (US$15.32) for unlimited web browsing (with usage monitoring over 200Mb per month) and two additional business tariffs. (release)