If you regularly make long-distance phone calls, chances are you've already used IP telephony without even knowing it. IP telephony, known in the industry as Voice-over IP (VoIP), is the transmission of telephone calls over a data network like one of the many networks that make up the Internet. While you probably have heard of VoIP, what you may not know is that many traditional telephone companies are already using it in the connections between their regional offices.

This person is using a computer to talk to a friend in another state.

In this article, you'll learn about VoIP and the technology that makes it possible. We'll talk about VoIP's major protocols, about the various services provided and the low-cost, often free software that allows you to take advantage of them.

But first, let's discuss the fundamental problem with existing telephone networks -- namely, their reliance on circuit switching.