The story behind the startup that grew to become the biggest mobile technology acquisition in Google's history begins five years ago in a small dorm room on the campus of the University of Pennsylvania. At the time, Omar Hamoui was pursuing an MBA degree at Penn's prestigious Wharton School while struggling to kick-start fotochatter, a mobile social networking startup that lets users share photos with friends. The challenge was reaching consumers: Online advertising for a mobile service was not only impractical, it was also prohibitively expensive--Hamoui calculates that the time and money spent marketing the company translated to customer acquisition costs of $30 per user. So he turned to the emerging mobile web instead, paying sites a penny per click to promote the fotochatter solution. "About 10 percent of people who clicked the mobile ad signed up for the service," Hamoui recalls. "Our customer acquisition cost dropped from $30 to 10 cents overnight."