The Session Initiation Protocol (SIP) is taking the telecom and data industry by storm. Everyone is talking about it. MCI is deploying services on top of SIP. We take a fundamental look at this protocol and its impact on the VoIP market place. Vovida Open Communication Application Library (VOCAL) is an open source, SIP-centric, toll quality, carrier grade communications software for next generation carriers and service providers. We examine its architecture, scalability, and reliability, and learn how to develop features on top of the platform.