Make a server.
Have it accept a "registration" packet which includes a geographic location and a channel number. Until a later "logout", it gets sent a constant stream of live audio (maybe RTP based).
It can, at any time, send to the server an audio stream.
The audio it gets is a mix of all incoming audio on the same channel where the level (amplitude) of the audio included is based on the relative proximity of the geographic location from which the incoming audio streams arrive and the listener.
What have you got?
CB/Ham AM radio simulator over IP!
Anyone want to make an RFC?
Could this be the new twitter? Imagine the phone app, push to talk, always streaming audio, location update as you move...