Abstract: Personal Mobile Communication services are no longer limited by connection-oriented network access to the services that network service nodes are able to offer. Given the ability to deliver services using end-to-end IP connectivity - notably over wireless links - will cause services to move out to the mobile end-devices. In addition, IP enables us to use multiple services over the same link. Consequently, we need ways to enable the end-devices to deal with the greater degrees of freedom, when our personal communication allows us to use any combination of services that may be running in other end-devices. With short-range radio links, our need to make use of and deal with spontaneous connectivity increases even further. In this paper, a novel eXtensible Service Protocol (XSP) is described. After examining its properties, we look at how it can enable ad-hoc mobile applications, as well as enabling adapting applications to the conditions and context of the communication.