iirc, one part of the rtcom beta can use bonjour/zeroconf to set up ad-hoc im within a subnet. beyond that it would have been interesting if someone would come up with a kind of digital "bc" radio system for general broadcast data exchange. it would be more like udp then tcp tho, and one would probably have to forgo ip fully, given the setup overhead.
same goes for ad-hoc wifi as i think its limited to 1 to 1 connections, much like a ethernet crossover cable...