The co-founder of smartphone software phenomenon Foursquare talks with Bloomberg BusinessWeek's Arik Hesseldahl about why so many people are "checking in" everywhere they go
Learn how companies including Coca-Cola, Unilever and American Express are trying to reach customers on smartphones in an advertising market set to quintuple to $18.3 billion by 2015. Their strategy could spell profits for mobile ad players including Facebook, Google and Twitter