A PBX (Private Branch Exchange) is a system that connects telephone extensions to the Public Switched Telephone Network and provides internal communication for a business. An IP PBX is a PBX with Internet Protocol connectivity and may provide additional audio, video, or instant messaging communication utilizing the TCP/IP protocol stack
A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals suitable for transmission via cables or other transmission media over long distances, and replays such signals simultaneously in audible form to its user.
Videoconferencing (VC) is the conduct of a videoconference (also known as a video conference or video teleconference) by a set of telecommunication technologies which allow two or more locations to communicate by simultaneous two-way video and audio transmissions. It has also been called ‘visual collaboration’ and is a type of groupware.