For a while, mobile social software (MoSoSo) has automated the idea of affinity groups. But now businesses are noticing. Embraced early by as a way for cell-phone-toting singles to find each other, MoSoSo marries mobile-communications technology with a giant database. Dodgeball subscribers register groups of friends, squash mates and the like. Then they can send out a single text message to everyone on their list (or everyone who's a friend of a friend) within a geographic radius and call a "meeting" at, say, the local ball field.

Since it launched in May, Dodgeball has picked up 13,000 subscribers in 22 cities. To an advertiser, that's critical mass, and Absolut has started an ad campaign on the service. Users opt in as a "friend" and are notified when the company calls a party at a nearby bar. At MIT, researchers are playing around with Bluetooth-enabled conference badges and cell phones that will let attendees find colleagues with similar interests, says Alex Pentland of the school's Media Lab. He calls his software Serendipity, envisioning a world where strangers on a train with common interests would find each other. Pentland's future world isn't here yet. For full functionality, cell-phone users would have to register their relatives, resumes, hobbies and more. That raises privacy worries that may prevail over the appeal of the instant hookup.