Private Branch Exchange. Or PABX (Private Automatic Branch Exchange). In telephony, a PBX system behaves as a customer's premises over trunk lines (thus the term "branch"). At first, PBXs mimicked a small telephone company switchboard. Users would use an operator to take and make telephone calls to and from the PSTN (Public Switched Telephone Network). Over time, users were able to dial directly, without the use of an operator. Today, computer telephony platforms such as automated attendants are able to route incoming calls automatically.
