Impromptu is a mobile audio device which uses wireless Internet Protocol (IP) to access novel computer-mediated voice communication channels. These channels show the richness of IP-based communication as compared to conventional mobile telephony, adding audio processing and storage in the network, and flexible, user-centered call control protocols. These channels may be synchronous, asynchronous, or eventtriggered, or even change modes as a function of other user activity. The demands of these modes plus the need to navigate with an entirely non-visual user interface are met with a number of audio-oriented user interaction techniques.