Omar Hamoui only started his company in 2006, but chances are his fledgling project has already served an ad to your mobile phone. The so-called “mobile Web,” which refers to people browsing the Web on their portable devices, has been growing exponentially in recent years, and so has Hamoui’s playfully named company, AdMob (the “mob” is short for “mobile”).

From a company with a staff of one that served up several million ads in its first few months, AdMob has become a 60-person powerhouse that serves almost 3 billion targeted ads a month to mobile devices worldwide. It is funded by $19 million in venture capital from, among others, Sequoia Capital, the Silicon Valley firm that’s backed companies like Google and Yahoo. In classic long-tail fashion, Hamoui has succeeded by signing up thousands of mobile websites as publishers and making it easy to serve up ads targeted by mobile device, user’s geographic location, and type of content an almost entirely automated process.

As Hamoui has gobbled up share in a market that could grow as big as $4 billion in the U.S. alone by 2011, the dominant sellers of online ads have largely been on the sidelines—until now.

Last September, Google rolled out a product for its current advertisers who want to place ads on portable devices called AdSense for Mobile. This extended Google’s search-results ads to the Web. AdSense for Mobile increases its service for publishers. According to Google, the number of Google searches being done on mobile devices is growing rapidly, and is likely to increase as the company develops mobile products for the iPhone and others.
    
Google’s not the only giant circling around AdMob’s market. AOL acquired one of AdMob’s strongest competitors, Third Screen Media, last year, while Microsoft, Yahoo, and Nokia have all also acquired smaller AdMob competitors in recent months. The advantage of some of these competitors, particularly Third Screen, is in their relationships with big-name publishers that have wider reach than the typical AdMob publisher.

It’s shaping up as a classic David versus Goliath battle, pitting the fresh-faced, serial entrepreneur Hamoui against some of the Silicon Valley establishment.

But the 31-year-old Hamoui, who dropped out of the Wharton School after his first year to run and grow AdMob, says he’s ready for the fight.
 
“They have lots of money and lots of people,” he says of Google. “But we can move fast and react to changes quicker than a large company can.”