Dennis Crowley and Alex Rainert have launched Dodgeball 3.0, a location based mobile messaging solution for New Yorkers.

Dodgeball has three core features: Guide, Circles, and Scout. Guide is just for finding and rating places, Circles and Scout are much more interesting because they are community based. Circles is ìI am here. Where are you?î It gives you the mailing list pattern for location: group re-direct of of your location to people in your Circle. Scout is ìWhat is going on near me?î It gives you the ability to shout a message to any subscriber in a 10 block radius, and to listen to other messages broadcast in that same area.

The catch is that you have to tell Dodgeball where you are when you want to use the service. Once applications like this can leverage true mobile positioning (GPS, Triangulation or just plain old Cell ID), the fun will really begin!