Probably old hat for readers of this site, but if you’re looking for something to point your boss at to explain all this VoIP stuff, Ted Wallingford has written an excellent summary in his O’Reilly Network article, What is VoIP?
Ted covers the different technologies that make up VoIP, as well as looks at some of the reasons for it’s growing popularity and where the technoloy is headed. Ted knows of what he speaks, he’s the author of Switching to VoIP, which has been getting rave reviews as a hands-on practical guide for telecom professionals making the switch.
Voice over Internet Protocol (VoIP) is the family of technologies that allow IP networks to be used for voice applications, such as telephony, voice instant messaging, and teleconferencing. VoIP entails solutions at almost every layer of an IP network–from specialized voice applications (like Skype) all the way down to low-level quality measures that keep those applications running smoothly.