A private automatic branch exchange (PABX) is an automatic telephone switching system within a private enterprise. Originally, such systems - called private branch exchanges (PBX) - required the use of a live operator. Since almost all private branch exchanges today are automatic, the abbreviation "PBX" usually implies a "PABX."
EPABX is an abbreviation that stands for Electronic Private Automatic Branch Exchange. It comes under the category of business phone systems which serve a business environment. It is an office equipment of immense use for telephonic connectivity with extensions of a single phone line.
An IP PBX 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 system with IP connectivity and may provide additional audio, video, or instant messaging communication utilizing the TCP/IP protocol stack.