I worked on a very similar idea for a while though admittedly failed to polish and market appropriately to gauge interest. I thought about a lot of the "issues" that people are bringing up here. My idea was mainly to try and emulate a digital CB radio. So you'd have the overlap issue as mentioned by nilkn, but I didn't see this as a problem in accomplishing the main objective. The main objective being to permit local, real-time communication. Why is the high way backed up to a stand still? Hop on local chat. Where is a good place to park for the outdoor concert? Hop on local chat. I'm new in the area and can't find 'blah' street. Ask on local chat.