This paper presents an approach for using ontologies to both organize knowledge and facilitate knowledge sharing among service and user interface agents in a multi-agent personal communication system. These systems are designed to manage a user’s diverse and heterogeneous communication services. The nature of this domain and the user requirements of mobile, highly personalized services make a multi-agent solution particularly attractive. Multi-agent personal communication systems have “service adapter” agents that communicate with “personal communication” interface agents that represent the user’s communication preferences. The paper describes the use of ontologies for the partitioning of knowledge to facilitate the programming of multi-agent personal communication systems and the use of a client/server model for knowledge sharing among the service adapter and personal communication agents. Meta-knowledge is used for specifying to the personal communication agents the structure of the knowledge they are to receive from the service adapter agents.