Reuters reports that NTT DoCoMo is gearing up to add yet more names to its stable of mobile search companies, bringing the total to 13 providers. The surprise is the inclusion of Yahoo, which is also 41% owned by rival Softbank. Earlier, Softbank bought Vodafone’s Japanese activities, making Softbank the owner of the country’s number three mobile operator and one of DoCoMo’s biggest headaches. KDDI, the number two Japanese mobile operator, has tied up with Google for mobile search. DoCoMo’s approach to mobile search, which it unveiled in July, allows users to perform keyword searches from the top page of the Japanese iMenu portal, and lists those results along with links to the results served up by nine search engines (MSN Search, Infoseek Mobile, R25shiki Mobile, CROOZ!, F*Route, Seafly, OH!NEW?, Livedoor mobile and goo). Reuters further reports that DoCoMo has said it will offer Google, although I can’t get a confirmation of this. No matter the number, DoCoMo’s example demonstrates that an open approach to mobile search can also be a winning one, and it’s not just about mobile operators. On the vendor side of the equation, Nokia continues to collect partners and expand its ecosystem of mobile search providers. After all, just as users rebel against closed mobile portals and closed operating systems, so might they also vote with their feet if they feel locked into one mobile search provider on the phone or the mobile Web.