A french company has developed technology that turns a mobile/cellular phone into a p2p network. The Technology will allow users to make their music files available to anyone on the phone network potentially creating a vast p2p network. With 3G just around the corner in Europe, P2P is one application that I can see been successful with high-speed mobile networks.
http://news.bbc.co.uk/1/hi/technology/2253185.stm