The advent of deregulation combined with new oppotunities opened by advances in telecommunications technologies has significantly the paradigm of telecommunications services, leading to a dramatic increase in the number and type of services that telecommunication companies can offer. Building new advanced multimedia telecommunications services in a distributed and heterogeneous environment is very difficult, unless there is a methodology to support the entire service development process in a structured and systematic manner, and assist and constrain service designers and developers by setting out goals and providing specific means to achieve these goals. Therefore, in this paper, after a brief presentation of a proposed service creation methodology, its service design phase is examined in detail focusing on the essential activities and artifacts. In this process, the exploitation of important service engineering techniques and UML modelling principles is especially considered. Finally, alternative and complementary approaches for service design are highlighted and a validation attempt is briefly outlined.