Recent advances in wireless communication technologies have attracted ad hoc networking, which enables mobile users to communicate with each other without any infrastructure. While many ad hoc routing protocols have been proposed, ad hoc communication and its applications are not widespread. The handiest wireless devices, namely, mobile phone terminals, are expected to expedite widespread use of ad hoc communications. More mobile phones have been equipped with short distance wireless interfaces such as wireless LAN and Bluetooth. When ad hoc communication is realized on such mobile phones with these wireless interfaces, ad hoc communications will be available anytime, anywhere, which we believe will become a driving force for ad hoc networking technology. However, although the performance of mobile phones has improved greatly over the past several years, their resources are still limited compared to laptop PCs. In this paper, we first present design principles for mobile ad hoc communications based on cases of assumed use. According to the design principles, we implement ad hoc networking protocols as well as their applications on mobile phones to verify their effectiveness. Based on the results of evaluations, we discuss the performance characteristics and potential application areas.