Submitted: Jul 8, 2008 - The mobile ad business has barely gotten off the ground, but it's already got an early winner: AdMob, a mobile ad network that serves up some 3 billion impressions a month. VentureBeat's Matt Marshall thinks the company is close to breaking even on about $14 million in net revenue. In a few years, Matt figures, AdMob will be an IPO candidate.

Our worry: That in a few years, AdMob will find…