In short
PBX vs VoIP compares two different things. A PBX (private branch exchange) is the switching system that routes a business's calls between extensions and outside lines. VoIP is the technology that carries calls as data over an IP network. An IP PBX, hosted PBX or cloud phone system is simply a PBX that uses VoIP.
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The short answer
The NCSC defines a Private Branch Exchange (PBX) as "a telecommunications system used to manage and route incoming and outgoing telephone calls within an organisation". It is the brain of a business phone system: extensions, transfers, hunt groups, queues, menus, voicemail and the connection to outside lines.
VoIP (voice over IP) is a transport. It turns speech into data packets and carries them over an IP network instead of copper phone wiring.
So the difference between PBX and VoIP is the difference between the switchboard and the wires. Older PBXs used dedicated telephone cabling and ISDN or analogue lines. Modern PBXs use VoIP, whether they sit in your comms room, run on a virtual server or are delivered from the cloud. When people compare "PBX vs VoIP", they usually mean an old on-site PBX against a modern VoIP phone system.
Types of PBX compared
The NCSC's PBX best practice guidance describes five types of PBX. This table summarises its definitions and adds how each relates to VoIP.
| Type | What it is (NCSC) | Uses VoIP? | Where it runs |
|---|---|---|---|
| Traditional PBX | Hardware-based, with physical switches and cables connecting each user to the PBX equipment | No; analogue or digital handsets and lines | Your premises |
| IP PBX | Also known as VoIP PBX: a digital PBX that sends calls as data packets over the organisation's existing data network | Yes | Your premises, on a server or appliance |
| Hosted or cloud PBX | The PBX hardware and software are hosted off site by a service provider, and you connect over the internet | Yes | The provider's data centre |
| Virtual PBX | A software PBX on virtualised servers; a subset of IP PBX, deployed on premises or in the cloud | Yes | Your virtual servers or a cloud account |
| Hybrid PBX | Combines traditional and IP PBX, for organisations moving to IP gradually while still using existing analogue or digital lines | Partly | Your premises |
The NCSC also notes that IP PBX systems can use the existing data network, and Wi-Fi, to reduce installation and maintenance costs, and that hosted PBX is particularly attractive to small and medium-sized organisations that want advanced features without the infrastructure.
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Traditional PBX vs a VoIP phone system
| Traditional PBX | VoIP phone system (IP, virtual or cloud PBX) | |
|---|---|---|
| Cabling | Dedicated telephone wiring to every user | Shares the data network; desk phones can be powered over the network cable |
| Outside lines | ISDN or analogue lines from the exchange | SIP trunks, or the provider's connection to the phone network |
| Handsets | System phones made for that PBX | IP desk phones, DECT, softphones and mobile apps |
| Remote and hybrid working | Diverts to mobiles | Users sign in anywhere with an app or phone |
| Growth | Line cards, ports and licences on the box | Add users and sites in software |
| After January 2027 | Openreach says ISDN services must move to IP by January 2027 or be ceased | Already IP |
Many traditional and hybrid PBXs can carry on for a while through an ISDN-to-SIP gateway or a software upgrade that adds SIP. Our guide to ISDN to VoIP sets out those routes, and switching from landline to VoIP covers the wider move.
Virtual PBX vs VoIP, and cloud PBX vs VoIP
These two comparisons cause the most confusion, because both are already VoIP.
Virtual PBX. In the NCSC's definition, a virtual PBX is PBX software running on virtualised servers, a subset of IP PBX, deployed on premises or in the cloud. 3CX is a good example of the flexibility: 3CX says you can choose Windows or Linux, hosted by 3CX or self-hosted on Amazon, DigitalOcean, Azure or Google, and its commercial editions use one annual licence per system, sized by simultaneous calls. In marketing, "virtual PBX" is sometimes used more loosely to mean any hosted service, so it is worth asking where the software actually runs.
Cloud PBX. A cloud or hosted PBX is a PBX delivered as a service. Microsoft describes Teams Phone as its technology for "call control and Private Branch Exchange (PBX) capabilities in the Microsoft 365 cloud". Webex Calling is Cisco's cloud calling platform, and Forever UC is built on Cisco BroadSoft technology. Our sister site explains what is hosted PBX in detail.
In both cases the PBX does the routing and VoIP does the carrying. The real choice is where the PBX runs and who looks after it.
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IP PBX or hosted: which fits?
Where your PBX runs changes cost profile, responsibility and resilience more than features. As a rough guide:
- Hosted or cloud PBX suits most organisations moving off ISDN or an ageing system, especially with home workers or several sites. The provider runs the platform and you use phones and apps over the internet.
- IP or virtual PBX on your own servers suits organisations with a recent, supported system, in-house skills, or integrations that need a PBX on site. It connects to the phone network through SIP trunks.
- Keeping your PBX alongside Teams is possible too. Dstny's Direct Routing service connects Microsoft Teams users to an existing SIP-capable PBX or SIP trunk with nothing installed on site; each user needs Teams Phone Standard. See Teams Direct Routing.
Our sister site's comparison of hosted vs on-premise phone system options goes through cost profile, maintenance and survivability, and our guide to the best VoIP phone system helps you match a platform to how you work. Forever Group's main site covers on-site PBX systems and their support.
Securing a PBX, whichever type you choose
The NCSC is clear that the PBX owner is responsible for the security of the phone system, and that if it is abused for dial-through fraud, the business "will be expected to pay the bill". Its recommended controls apply to every type:
- Change default passwords and admin codes, use strong passwords and remove unused accounts
- Use multi-factor authentication for administrative access
- Lock firewall rules down to trusted IP addresses, such as your SIP trunk provider
- Keep PBX software and VoIP phone firmware patched, with automatic updates where possible
- Use TLS between PBX components, and TLS and SRTP on hosted systems
- Limit dialling: disable international and premium-rate calls you do not need
For an on-premise PBX, the NCSC also recommends isolating it on its own VLAN or subnet. Our VoIP security guide covers each control and the risks behind them.
How we help
Forever Systems supplies both sides of this choice: hosted platforms, including hosted 3CX, Microsoft Teams Phone, Webex Calling, Forever UC and Forever Teams, and SIP trunks for PBXs you keep. Our guides to 3CX VoIP, Teams VoIP and Webex VoIP explain each platform. We can start by auditing your current system, lines and connected devices, then recommend whether to keep, connect or replace it.
Contact us with your PBX make, how many users and lines you have and when its support ends, and we can set out the options side by side.
How Forever Systems helps you choose a VoIP phone system
We supply and support several VoIP platforms, so we can recommend the one that fits how your team takes calls rather than fitting your business around one product.
- Platform advice across hosted 3CX, Microsoft Teams Phone, Webex Calling, Forever UC and Forever Teams, with SIP trunks for phone systems you already own
- A requirements check of your broadband, network and routers before anything goes live
- Numbers and porting: we can help you keep your existing business numbers and plan the move away from analogue and ISDN lines
- Handsets and headsets that suit each platform, bought outright or, in some cases, included in your monthly rental, with the options confirmed at quote
- Set-up and changes: call flows, users and devices configured for you, and help with moves, adds and changes afterwards
- For BT Cloud Voice, see our sister site cloudvoice.cloud, and for hosted and cloud platforms in depth, cloudphone.cloud
We work with businesses, schools, charities and public sector organisations.
Frequently asked questions
What is the difference between PBX and VoIP?
A PBX is the system that routes calls between extensions and outside lines. VoIP is the technology that carries calls as data over an IP network. A modern IP PBX or cloud PBX is a PBX that uses VoIP, so most businesses today have both in one system.
Is a PBX the same as VoIP?
No. A PBX is the switching system; VoIP is the transport. A traditional PBX used telephone wiring and ISDN or analogue lines, while an IP PBX, also called a VoIP PBX, carries calls over the data network.
What is the difference between a virtual PBX and VoIP?
A virtual PBX is PBX software running on virtualised servers, on premises or in the cloud, and it uses VoIP to carry calls. The NCSC describes it as a subset of IP PBX. VoIP is the underlying technology rather than a type of PBX.
Is an IP PBX the same as a VoIP PBX?
Yes. The NCSC uses the two terms for the same thing: a digital PBX that uses internet protocol to carry voice as data over the organisation's network.
Cloud PBX vs VoIP: which do I need?
A cloud PBX is a VoIP phone system run by a provider in its data centre, so choosing one means choosing VoIP. The decision is between running the PBX yourself, on site or on virtual servers, and having a provider run it for you.
Can I keep my existing PBX and still use VoIP?
Often, yes. A PBX that supports SIP, or can be fitted with a gateway, can replace its ISDN or analogue lines with SIP trunks. Teams users can also be connected to an existing SIP-capable PBX through a Direct Routing service.
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More VoIP phone system guides
3CX VoIP3CX as a VoIP PBX: where it runs, the editions, licensing and SIP trunks.