Centrex is a portmanteau of central exchange, a kind of telephone exchange.wikipedia
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Business telephone system

PBXprivate branch exchangekey telephone system
It provides functions similar to a PBX, but is provisioned with equipment owned by, and located at, the telephone company premises.
From the 1960s a simulated PBX known as Centrex provided similar features from the central telephone exchange.

Telephone exchange

exchangescentral officeexchange
Centrex is a portmanteau of central exchange, a kind of telephone exchange.

Financial District, Manhattan

Financial DistrictWall StreetJohn Street
Centrex service was first installed in the early 1960's in New York's financial district by New York Telelphone.

Call forwarding

forwardingCall divertCall Forward on Busy
Call forwarding

Conference call

conference callingconference callsaudio conferencing
Conference calling

Last-call return

*691471call return
Last-call return, automatic recall, or (on PBX and centrex service) camp-on, is a telecommunication feature offered by telephony service providers to subscribers to provide the subscriber with the telephone number, and sometimes the time, of the last caller.

CLLI code

Entities within client-owned buildings (such as Centrex installations) are coded in the same format as telephone company buildings.

Attendant console

An attendant console is a telephone station that is generally part of a private branch exchange (PBX) or Centrex or other private telephone system.

War dialing

wardialingwar dialerwardial
If a human or answering machine answers, the wardialer program hangs up. Depending on the time of day, wardialing 10,000 numbers in a given area code might annoy dozens or hundreds of people, some who attempt and fail to answer a phone in two rings, and some who succeed, only to hear the wardialing modem's carrier tone and hang up. The repeated incoming calls are especially annoying to businesses that have many consecutively numbered lines in the exchange, such as used with a Centrex telephone system.


remote switching centreDMS-250
It provides Plain Old Telephone Service (POTS), mobility management for cellular phone systems, sophisticated business services such as Automatic Call Distribution (ACD), Integrated Services Digital Network (ISDN), and Meridian Digital Centrex (MDC), formerly called Integrated Business Network (IBN).


NFON operates IP-Centrex-telephone systems for businesses and is the only provider of cloud telephony that offers this service specifically for large businesses with 1-249,000 extensions.

Extension (telephone)

extensionextensionsextension number
In business telephony, a telephone extension may refer to a phone on an internal telephone line attached to a private branch exchange (PBX) or Centrex system.


Cirpack is an NGN (Next Generation Network), SBC (Session Border Controller) and IMS vendor for Telecommunications Operators, Internet and Application Service Providers, focusing on telephony services such as residential and business VoIP, IP Centrex, SIP Trunking, Triple play, Fixed Mobile Convergence, VoLTE, Transcoding etc.

Intelligent Network

INIntelligent Network (IN)IN platform
Centrex service (Virtual PBX)

Number pooling

The change also caused problems for some office private branch exchange systems, creating an opportunity readily exploited by vendors to sell businesses costly new equipment or hosted Centrex service.

Line hunting

hunt grouphunt groupsHunting
Also, some phone companies will provide this feature for a small fee (see also: Centrex).

Number Five Crossbar Switching System

5XB switch5XBNo. 5 Crossbar switch
Each vertical group is divided into five vertical files of ten lines, important because class of service, or customer group identification in later Centrex offices, is shared by all ten lines in the vertical file.


It pioneered the use of "Centrex ISDN" which is a 24x7 dedicated flat-rate ISDN line.

Winnipeg Tribune

Winnipeg Daily TribuneWinnipeg Evening Tribune
On Sunday, June 21, 1970 a new Centrex telephone system was installed for advertisers and subscribers to use when calling.

Via Net Loss

Government subscribers include cities, counties, state, and federal agencies and often included Centrex service.

Plain old telephone service

POTSLocal Telephone Servicetelephone
The services include voicemail, Caller ID, call waiting, speed dialing, conference calls (three-way calling), enhanced 911, and Centrex services.