What is a PBX?
A PBX (Private Branch Exchange) is a private telephone system that connects the phones inside an organization and links them to the outside telephone network. It handles internal extensions, transfers, voicemail and routing of incoming calls.
How it works
A PBX sits between the company's phones and the carrier. Internal calls between extensions stay inside the PBX; external calls go out over a limited number of shared lines or trunks.
Traditional PBXs were hardware boxes in a server room wired to analog or digital phones. IP PBXs run on servers and use VoIP, and a cloud PBX moves the whole system to a provider's data center.
The PBX holds the rules: who rings when a number is dialed, what the menu says, where calls go after hours and which voicemail box takes a missed call.
Why it matters
01Extensions
Staff reach each other with short internal numbers, free of charge.
02Shared lines
Many employees share a smaller number of outside lines.
03Professional handling
Menus, transfers and queues make callers feel they reached a company, not a person's mobile.
Allo and PBX
Allo replaces an office PBX with a cloud phone system: numbers, routing, IVR and transfers in an app, with no hardware to install.
Related terms
The terms that usually come up in the same conversation.
All glossary terms
SIP trunking
Virtual lines that connect a PBX to the phone network over the internet.
Read the definition
Frequently asked questions
A PABX (Private Automatic Branch Exchange) is a PBX that switches calls automatically instead of through a human operator. Today every PBX is automatic, so the terms mean the same thing.
They need what a PBX does, such as shared numbers, transfers and menus. Most now get it as a cloud service instead of buying hardware.
A PBX run by a provider in its data center and accessed over the internet. It is another name for a cloud PBX.