Voice over Internet Protocol (or VoIP) is on the verge of revolutionising the telecommunications industry. It is a totally new way of carrying voice traffic, and one that telecommunications companies will have no choice but to fully embrace if they are to remain competitive. Until recently, all voice traffic has been carried using what is called circuit switched technology in which a physical circuit is switched to provide a call for a user. The radically new approach owes much to the overwhelming success of the Internet, which paved the way for the adoption of packet data communications based on Internet Protocol (IP). The concept of voice over IP is quite straightforward. An endpoint - which may be a VoIP phone or a computer - consists of a few blocks. A vocoder converts the analogue audio to and from a digital format. The data generated is split into packets and sent, with the relevant protocol, into the outside world via a network interface card. Signalling and call control are also applied through this card. The article outlines the the basic operation of VoIP.