An IP (Internet Protocol) PBX (Private_branch_exchange) is a business telephone system designed to deliver voice or video over a data network and interoperate with the normal PSTN (Public Switched Telephone Network).
VoIP (Voice over Internet Protocol) gateways can be combined with traditional PBX functionality enabling businesses to use their managed intranet to help reduce long distance expenses, enjoy the benefits of a single network for voice and data and advanced CTI (Computer Telephony Integration) features or be used on a pure IP system which in most cases give greater cost savings, greater mobility, and increased redundancy.
An IP-PBX can exist as a hardware object, or virtually, as a software system.