An IP PBX, Unified Communication System or business phone system, a PBX acts as the central switching system for phone calls within a business. PBX systems handle internal traffic between stations and act as the window to the outside world. An IP PBX or IP Phone System replaces a traditional PBX or phone system and gives employees an extension number, the ability to conference, transfer and dial other colleagues. All calls are sent via data packets over a data network instead of the traditional phone network. You can connect existing phone lines to the IP PBX and make and receive phone calls via a regular PSTN line.