Implementation of real-time telephone-quality voice2 transmission using the Internet protocol (IP, the Internet Engineering Task Force’s [IETF’s] request for comment [RFC] 2460 and RFC 791) is no longer as challenging a task as it was a few years ago [1,2]. In this introductory chapter, I define the instances and interfaces of both public switched telephone networks (PSTN) and corporate or enterprise communication networks where voice over IP (VoIP) can be implemented. The goals of VoIP implement