It’s an alliance that began when two geeky 13-year-old pals in a northwest London suburb started trudging their heavy desktop PCs over to each other’s houses to play games like Duke Nukem 3D, Unreal Tournament, and Red Alert.

Fifteen years later, after following each other to the University of Cambridge and later, San Francisco, Jude Gomila and Immad Akhund now run what could be the world’s largest mobile gaming community.

Heyzap melds social networking and games--like Zynga did on Facebook--but adds the where-it’s-at component of mobile. While Gomila and Akhund originally founded the company as an online destination where developers could distribute their games, they soon realized the majority of people were going to be playing them on their phones.

It was a good call. More than 6 million people have downloaded the Heyzap app to their iPhones or Android smartphones. It lets them check into games (like you check into a physical location on Foursquare), discover which ones are being played by friends, leave, or browse tips on playing, and earn badges. Users can also find, follow, and message friends who play their favorite games or only people checking in from various locations.

Gomila, who has had the uncommon honor of guest blogging for Ashton Kutcher, sees Heyzap as building the social gaming graph for mobile just as some big guns have done in other spaces, such as Instagram with photos, Socialcam with video, and Foursquare with location. “No one’s really attacked the gaming graph before in a direct way, so we’re doing that right now and the app is growing really really fast,” he says.

Heyzap’s business model is based on Cost-Per-Install (CPI) advertising. Just like Google gets paid every time someone performing a search clicks on an AdWords ad, developers hire Heyzap to get users to install their games.  The beauty, according to Gomila, is of the 200,000 games available at Apple’s App Store and Google Play, Heyzap’s recommendation engine only shows users titles they’re likely to want. “We can actually get the user what kinds of games they’re really looking for because we know what they’re downloading in the first place and what their gaming habits are,” he says.

“We are also continually iterating and pushing the Heyzap app forward,” says Akhund. “In the last year and a half we have done 91 separate releases off the app, which is more than once a week. That’s a pretty insane rate of iteration for mobile.”

Silicon Valley loves Heyzap, a Y Combinator alumni. Investors include Union Square Ventures as well as angels and entrepreneurs Naval Ravikant, Joshua Schachter, Chris Dixon, and Christina Brodbeck.

Albert Wenger, partner at Union Square Ventures, says Akhund is the kind engineer-entrepreneur his firm loves to back. “He not only comes up with great ideas but can build the v1 often literally overnight!” he says.

Heyzap launched its mobile app at the start of 2011 and last year raked in $2.2 million in revenues. In 2012 Gomila and Akhund expect to see that number rise to $10 million.