Google announced today it would acquire mobile display ad serving platform AdMob for $750M in stock. AdMob is a 3-year-old San Mateo-based startup founded by Omar Hamoui. AdMob is a mobile advertising firm serveing ads on mobile websites and applications. It’s current clients include Ford Motors, Coca-Cola, Electronic Art, Procter & Gamble, MTV Europe, Adidas AG and Paramount Pictures.

This might turn out to be a risky gamble by Google as it tries to prevent competitor from entering the mobile advertising domain by overpaying for AdMob. It’s estimated that AdMob’s current revenue is $45 to $68 millions per year. However, Google currently already owns a major stake in mobile advertising with DoubleClick Mobile unit.

Both AdMob and Google have estimated that the volume and effectiveness of mobile advertising in constantly rising. In a recent report, AdMob said that the number of mobile ads it served had increased nearly 540% from September 2007, to 10.2 billion per month from 1.6 billion. Google confirmed that the number of searches performed by smartphone users has increased by a factor of five over the last two years. It estimates that the marketer spending on mobile advertising is growing at 30% annually.

The deal still need to be approved by regulatory agencies, but Google hopes it can be done within a month.