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Yahoo is expected to announce today that it is creating a mobile advertising network geared to cell phones. The service will allow marketers to place ads both on Yahoo's mobile services and on those of other publishers.

Yahoo's network of publishers consists, for now, of three web services: MobiTV (a video service to be used with cell phones); Opera, a maker of web browsers; and Go2, a Yellow Pages site, the New York Times writes (via MediaBuyerPlanner). But Yahoo plans to quickly expand its network over the next few months.

Yahoo's mobile ad network will focus on publishers and advertisers, groups essential to the success of the mobile internet. By summer, Yahoo will begin delivering text, display and video advertising on third-party mobile websites, according to Steve Boom, Yahoo SVP for broadband and mobile.

Yahoo has been aggressively pursuing the mobile market and in January began promoting its new mobile search software called oneSearch, which allows users to find information such as sports scores and weather reports without having to scroll through a long list of sites.

Yahoo has fallen behind Google in internet search. But Kevin Heisler, an analyst at Jupiter Research, says "one area where Google has not outshined Yahoo is mobile search."

The Yahoo Mobile Ad Network website is designed to give publishers one-stop shopping, writes Search Engine Land.