Private Branch Exchange (PBX)
A Private Branch Exchange (PBX) is a company's private telephone switch, connecting internal extensions to each other and out to the public phone network.
Definition
A Private Branch Exchange (PBX) is a company's private telephone switch, connecting internal extensions to each other and out to the public phone network. It owns the numbering plan, the hold queues, the menus, and the trunk lines to the carrier. Dial four digits and the call never leaves the building.
A PBX is not a Salesforce feature. It sits outside the platform, and Salesforce reaches it through a telephony integration layer. Open CTI covers older call centers, and Salesforce Voice with Partner Telephony covers anything built today. That layer turns a ringing phone into a screen pop and a logged activity.
The split matters when something breaks. Routing and audio belong to the phone system. Record matching and the call log belong to Salesforce.
In plain English
“Picture an office with one main phone number and two hundred desks. The private phone system is the switchboard in the back room. It answers the main number and decides which desk rings. Salesforce watches that switchboard and opens the right customer file the second a call lands.”
Worked example
A 200-seat insurance brokerage runs an on-premises IP PBX with staff extensions in the 4000 range and eight trunks to its carrier. A policyholder dials the main line, the PBX answers, plays its menu, and sends the call to the Claims queue. The brokerage's telephony vendor ships a managed package that registers a Partner Telephony contact center in Salesforce. When the call lands on extension 4127, Salesforce receives the caller ID 415-555-0142 and searches the Contact object on Phone. Maria Delgado's record opens next to her open Case 00043912. The agent picks up already reading the claim. On hangup, Salesforce writes a Task with Subject Inbound Call, CallDurationInSeconds 214, and WhoId pointing at Maria.
Where the PBX ends and Salesforce begins
What the phone system actually owns
Instead of buying a carrier line for every employee, a company runs one switch holding a pool of internal extensions and a smaller pool of outside trunks. Dial a colleague's extension and the PBX connects you internally. Dial the main number from outside and it answers, applies its rules, and rings a queue. Older units were boxes in a wiring closet running analog or digital lines. Almost everything sold now is an IP PBX, carrying calls as data over the network using VoIP. That shift made CRM integration practical, because an IP system can publish call events to other software while keeping the audio to itself.
The two ways Salesforce hears about a call
The older path is Open CTI, a browser-based JavaScript API that wires a third-party phone system into Salesforce Call Center. An admin imports the vendor's call center definition file from Setup, under Call Centers in Quick Find. Next come user assignments and a softphone layout, which decides what Salesforce looks up when the phone rings. Agents get a softphone in the utility bar with no desktop adapter to install. The current path is Salesforce Voice with Partner Telephony. Install the provider's managed package from AppExchange, then enter Partner Telephony Setup in Quick Find to create the contact center. Calls then arrive as Omni-Channel work items rather than through a bolted-on panel.
Open CTI is on a clock, and the names have moved
Salesforce states it plainly on the Open CTI support policy page: the API is in maintenance mode, retires in February 2028, and gets no new features. Help articles pin the date at February 28, 2028. One sharper detail catches teams standing up fresh environments: Open CTI is now deprecated and unavailable for newly created Agentforce Service orgs. The replacement has been rebranded too. Service Cloud Voice is now Salesforce Voice, and the Trailhead badge that used to teach it carries the title Partner Contact Center. One product, three names still in circulation.
Where the screen pop quietly fails
Caller ID is the grey zone between the two sides. If the PBX passes 4155550142 and your Phone fields hold (415) 555-0142, the search matches nothing. Nobody gets an error. Agents just stop trusting the pop. Agree the format with your telephony vendor before go-live. Then test the calls nobody demos: a number no record holds, a transfer between extensions, a caller who hangs up inside the menu. Those three break more integrations than the happy path.
How organizations use Private Branch Exchange (PBX)
Keeps plant-to-plant calls on its own PBX and logs only outside calls in Salesforce, so internal chatter stays off the activity timeline.
Routes patient calls through its existing PBX so recorded audio stays on its own network, and uses Salesforce only for record matching and activity history.
Collects the account number in its PBX menu and passes it over, so the pop opens the account, not the caller's contact.
Trust & references
Cross-checked against the following references.
Straight from the source - Salesforce's reference material on Private Branch Exchange (PBX).
Hands-on resources to go deeper on Private Branch Exchange (PBX).
About the Author
Dipojjal Chakrabarti is a B2C Solution Architect with 29 Salesforce certifications and over 13 years in the Salesforce ecosystem. He writes and edits salesforcedictionary.com, published by KineticBit Inc., to help admins, developers, architects, and cert/interview candidates sharpen their fundamentals. More about Dipojjal.
Test your knowledge
+5 pts / dayQ1. Which part of a Salesforce phone integration decides how an inbound customer call reaches a queue before any agent sees it?
Q2. Salesforce recommends moving new telephony development off Open CTI and onto which product?
Q3. An org wants to keep its existing PBX and carrier while getting the native Salesforce Voice console experience. Which telephony model fits?
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