This paper describes a systematic approach to provide support at the user agent level for peer-to-peer based multimedia communications using SIP (Session Initiation Protocol). In a society that is becoming increasingly mobile, the advantages of engaging in interactive sessionswithout relying on central servers or infrastructure are clear. Yet, currently many user agents and devices have little support for peer-to-peer communications. In this paper, we motivate for the use of structured peer-to-peer protocols called DHTs, as a foundation for a peer-to-peerlayer. We introduce the concept of ''DHT plug-ins'' which assist in abstracting the interface between the higher level application and the proprietary APIs exposed by the underlying DHTs, allowing us to manipulate user agents with peer-to-peer logic. This embeddable-DHT concept allows these user agents to use different DHTs with one common interface and participate in multiple overlays. We show how an opensource SIP user agent was thus modified and how realtime communications were supported.