The seamless and flexible interconnection of the existing and emerging protocols and networks is essential to the success of the new generation mobile applications and services. For exploiting the functional diversity, we have developed a middleware for mobile devices called the Plug-and-Play Application Platform (PnPAP). We have previously studied the Session Initiation Protocol (SIP) as an interconnecting protocol for the PnPAP nodes. In this paper, we analyze the usage of a new variant of SIP called Peer-to-Peer SIP (P2P SIP) for this purpose. Our interconnection architecture utilizes layered (hierarchical) P2P SIP to establish a self-organizing, failure tolerant overlay signaling network between PnPAP nodes. Signaling latency and scalability of the layered P2P SIP signaling is compared in a simulation environment with both the traditional client-server SIP and fully distributed P2P SIP. Simulation results illustrate the benefits of the layered P2P SIP solution where only the supernodes participate to the DHT management, enabling light-weight peer node implementation for mobile nodes.