What is a Private Branch Exchange (PBX)?

Private Branch Exchange is an in-house telephone switching system that interconnects telephone extensions to each other as well as to the outside telephone network (PSTN). A PBX enables a single-line telephone set to gain access to one of a group of pooled (shared) trunks by dialing an 8 or 9 prefix. PBXs also include functions such as least cost routing for outside calls, call forwarding, conference calling and call accounting. Modern PBXs use all-digital methods for switching, but may support both analog and digital telephones and telephone lines. See IP PBX and WPBX. An Interactive Voice Response (IVR) system, or phone tree, can provide all the features offered through PBX.

In telephony, PBX is a system that 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 make telephone calls to the PSTN (public switched telephone network). Now, users dial directly, without using an operator. Computer telephony platforms such as automated attendants are able to route incoming calls automatically, too.