Short for Private Branch extension or Private Branch Exchange, PBX is a local telephone switching system used to serve a limited area such as a business. Users of the PBX are connected to a small number of outside lines for making external calls, thus saving on communication expenses.
The phone system is usually facilitated by a local group or person on site, but may also be administered remotely. PBXs can offer analog, digital, and VOIP, as well as many advanced services such as caller ID, voice mail, multiple phone lines, call recording, and service to large call centers. A few of the main PBX providers include Avaya, Cisco, Siemens, and Mitel.