The Session Initiation Protocol (SIP) is the de facto standard for multimedia multiparty sessions signalling in Next Generation Networks (NGN). It is the basis of a wide range of IP multimedia services. SIP as per its standard specifications and current usage relies on centralized servers. However, research has recently started on the integration of Peer-to-Peer (P2P) principles to SIP for harnessing the benefits of decentralization. We have contributed to this research by proposing a novel architecture for P2P SIP. The architecture is an overlay made up of a set of self-organized proxies and distributed registrars. Unlike the other architectures proposed so far, it does not extend SIP messages and is P2P middleware independent. This eases implementation, interoperability with legacy, and ensures portability. Moreover we will discuss the routing issues related to such environment. Indeed, we will present how routing can be handle effectively through different proxies in the overlay. Finally, we will discuss which mechanisms we are looking to use to ensure routing messages delivery in secure way in our P2PSIP network. Secure messages routing is needed due to the fact that Proxy and Registrar nodes can misbehave.