VoIP (Voice Over Internet Protocol) is a group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet telephony specifically refer to the provisioning of communications services over the public Internet, instead of via the public switched telephone network.
A private automatic branch exchange PABX is an automatic telephone switching system within a private enterprise. It is an automated system used by telephone operators or switchboard.
A voice conference, or teleconference, is an auditory only system that uses a multi-point conversation using a telephone.
Internet Protocol (IP) telephone systems are cost effective and available to people with a data infrastructure.