Dodgeball, the social networking tool for mobile phones, is expanding past NYC this weekend, becoming available in SF, LA, Boston, and Philadelphia as well. (Full disclosure: Dodgeball management, aka Dennis Crowley and Alex Rainert, were students of mine, so I’m both reporting and kvelling.)

The quickie description — ‘Friendster for Mobile Phones’ — makes the service graspable by potential users, but hides a lot of the complexity actually in the service — social networking, mobile carrier interoperability, geocoding, lightweight user alert systems, on and on. I’ve watched these guys putting an astonishing amount of thought and effort into this system for the last couple of years, and it’s heartening to see it paying off, especially as the mobile carriers still seem to deeply not get the social potential of their formerly point-to-point devices.