An IP PBX (Private branch exchange) is a business telephone system designed to deliver voice or video over a data network and interoperate with the normal Public Switched Telephone Network (PSTN).

VoIP (Voice over Internet Protocol) gateways can be combined with traditional PBX functionality enabling businesses to use their managed intranet

Intranet

An intranet is a computer network that uses Internet Protocol technology to securely share any part of an organization's information or network operating system within that organization. The term is used in contrast to internet, a network between organizations, and instead refers to a network...

 to help reduce long distance expenses, enjoy the benefits of a single network for voice and data and advanced CTI

Computer telephony integration

Computer telephony integration, also called computer–telephone integration or CTI, is a common name for any technology that allows interactions on a telephone and a computer to be integrated or coordinated...

 features or be used on a pure IP system which in most cases give greater cost savings, greater mobility, and increased redundancy.

An IP-PBX can exist as a hardware object, or virtually, as a software system.

Function

Because a major part of IP PBX functionality is provided in software, it is relatively inexpensive and makes it easy to add additional functionality, such as conferencing

Conference call

A conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party...

, XML-RPC

XML-RPC

XML-RPC is a remote procedure call protocol which uses XML to encode its calls and HTTP as a transport mechanism. "XML-RPC" also refers generically to the use of XML for remote procedure call, independently of the specific protocol...

 control of live calls, Interactive voice response

Interactive voice response

Interactive voice response is a technology that allows a computer to interact with humans through the use of voice and DTMF keypad inputs....

 (IVR), TTS

Speech synthesis

Speech synthesis is the artificial production of human speech. A computer system used for this purpose is called a speech synthesizer, and can be implemented in software or hardware...

/ASR

Speech recognition

Speech recognition converts spoken words to text. The term "voice recognition" is sometimes used to refer to recognition systems that must be trained to a particular speaker—as is the case for most desktop recognition software...

 (text to speech/automatic speech recognition), Public switched telephone network (PSTN) interconnection ability supporting both analog and digital circuits, Voice over IP protocols including SIP, Inter-Asterisk eXchange, H.323, Jingle (extension of XMPP protocol introduced by Google Talk) and others.

Features

(Features depend on system in place, some features require licenses or other software/hardware)

• Unlimited Extensions
• Unlimited Auto Attendants
• Unlimited Voicemail Boxes
• Cell Phone Integration
• Integrated/Overhead Paging (PA System)
• Remote Phones
• Advanced User Interface (including Find me/Follow Me, Unified Messaging, Call recordings, Voicemail .wav).
• Extension Groups
• Auto Provisioning
• Extension Range Flexibility
• Caller ID
  Caller ID
  Caller ID , also called calling line identification or calling number identification or Calling Line Identification Presentation , is a telephone service, available in analog and digital phone systems and most Voice over Internet Protocol applications, that transmits a caller's number to...
  
   Customization
• DID
  Direct Inward Dialing
  Direct inward dialing , also called direct dial-in in Europe and Oceania, is a feature offered by telephone companies for use with their customers' private branch exchange systems...
  
   Direct Inward Dialing
• Find Me/Follow Me
• Time of Day Routing
• Extension Call Recording
• On the Fly Recording
• Call Return
• Voicemail Callback
• Voicemail to Email
• SMS Voicemail notification
• Voicemail Web Access
• Voicemail Bypass
• Intuitive VoIP Ready
• Voicemail Blast Groups
• VoIP Ready
• Inbound Call Description
• VoIP Compression
• Outlook Integration
• Announcement Interface
• Call-out
• Call Pickup
• System Diagnositcs
• Multivendor Phone Options
• Analog Phone Support
• BYO Phones
• Call Parking
  Call parking
  Call park is a feature of some telephone systems that allows a person to put a call on hold at one telephone set and continue the conversation from any other telephone set....
  
  
• Call Barge
• Dial by Name Directory
• Powerful Reporting
• CRM Integration
• Remote Linked Servers
• Operator Console
• Custom Routing Rules
• Conference Rooms
• Outbound Dial Map
• Speed Dial Numbers
• Channel Bank Support
• Multiple Music on Hold
• Analog and Digital T1 Ready
• PSTN or Digital Failover
• NIS Routing
• Advanced Routing (IVR
  Interactive voice response
  Interactive voice response is a technology that allows a computer to interact with humans through the use of voice and DTMF keypad inputs....
  
  )
• Fast Pass
• Caller Position Notification
• Call Whisper
  Call Whisper
  Call Whisper, otherwise known as Call Screening, is a calling feature that often appears on Non-Geographic Telephony systems and hosted inbound call handling software. It involves the playing of a message to the called party when they have answered a call, during which time the calling party...
  
  
• Auto call forwarding
• Unified Messaging
• Call Screening
• ANI
  Automatic number identification
  Automatic number identification is a feature of telephony intelligent network services that permits subscribers to display or capture the billing telephone number of a calling party. In the United States it is part of Inward Wide Area Telephone Service . ANI service was created by AT&T for...
  
   Routing
• DNIS Routing
• Enhanced Mobility
• Custom VoIP Provider
• Professional Development
• Fax Support
• Fax to Email
• Fax PDF Support
• ACD Features
• Click to Dial
• Softphone
• Call Transfer
  Call transfer
  A call transfer is a telecommunications mechanism that enables a user to relocate an existing call to another phone or attendant console by using the transfer button and dialing the required location. The transferred call is either announced or unannounced....
  
  
• Call Conference
  Conference call
  A conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party...
  
  
• Live Monitoring