Hosted VoIP vs On-Premise PBX: Which Is Right for Your Business?
If your business phone system is due for a review — or if a looming contract renewal has forced the question — you will eventually land on one choice: keep (or buy) an on-premise PBX, or move to hosted VoIP.
This guide lays out both options honestly. On-premise PBX still has a place for certain organisations. But for most UK small and medium-sized businesses, the numbers and the practicalities point clearly in one direction.
What is an on-premise PBX?
A PBX (Private Branch Exchange) is the hardware that manages your internal phone network. An on-premise system means a physical box — or rack of hardware — installed in your building. Your lines come in, the PBX routes calls between extensions, and your staff pick up desk phones connected to it.
You own the hardware. Your IT team (or a contracted engineer) maintains it. When something breaks, it is your problem to fix.
Historically, on-premise PBX ran over ISDN or analogue lines. More modern versions can run over SIP trunks, which connects them to the internet. But the box is still on-site.
What is hosted VoIP?
Hosted VoIP — sometimes called cloud PBX — moves the phone system off your premises and into a data centre managed by your provider. There is no hardware in your building. Your staff use desk phones, softphones on their computers, or a mobile app, all connecting over your existing internet connection.
Your provider handles the infrastructure, the software updates, the redundancy, and the routing. You pay a monthly subscription per user. You never touch a server.
Cost: capex vs opex
This is usually where the comparison starts.
On-premise PBX carries significant upfront cost. Hardware for a small office might start around £2,000. For a business with 30 to 50 users, you are realistically looking at £8,000 to £20,000 or more — before installation, cabling, configuration, and staff training. On top of that, you will likely pay for an annual maintenance contract and face engineer callout charges whenever something goes wrong.
Per-user licensing, if required by the PBX vendor, adds further ongoing cost. And when the hardware reaches end-of-life, you buy again.
Hosted VoIP has no upfront hardware cost and no installation fee. You pay a fixed monthly amount per user. At VoIPninjas, that starts at £5.99 per user per month on our Ronin plan, up to £24.99 per user per month on Shogun for unlimited UK and international calls. You know exactly what you will spend each month.
For most SMBs, replacing a capital expenditure of £10,000–£20,000 with a predictable monthly subscription is a straightforward financial improvement.
Maintenance and reliability
On-premise PBX puts the maintenance burden on you. Hardware fails. Fans stop working. Drives corrupt. When the box goes down at 8:30 on a Monday morning, someone has to fix it — and that someone is either your internal IT team or a contractor you are paying to turn up.
Out-of-hours failures are particularly painful. If the system goes down on a Friday evening, you may be waiting until Monday for an engineer, or paying premium rates for an emergency callout.
Hosted VoIP removes that problem entirely. There is no on-site hardware to fail. Your provider maintains the infrastructure, applies updates, and manages redundancy. If a data centre has a hardware issue, failover happens automatically. You do not get a phone call from your provider asking you to reboot a server — you just keep making calls.
Scalability
On-premise: adding a new user to a PBX often means buying additional licences, configuring the system, and sometimes purchasing new hardware if you have hit capacity limits. Scaling down is worse — you have already bought the hardware, so shrinking your team does not reduce your costs.
Hosted: adding a user takes minutes. You log in to your account, provision the extension, and they are live. Removing a user is equally simple. You only pay for what you actually use each month.
For businesses in growth mode, or those with seasonal fluctuations, this flexibility has real value.
Remote and hybrid working
This has become non-negotiable for most businesses since 2020.
On-premise: extending a PBX to remote workers typically requires a VPN, SIP configuration, or both. It is technically achievable but adds complexity, increases the attack surface on your network, and often results in a degraded call experience. Not all PBX systems handle it gracefully.
Hosted VoIP: staff work from anywhere. The mobile app or softphone connects to the same system as the office phones. Same extension number, same call recording, same auto-attendant routing — regardless of whether someone is at their desk in the office or working from home in another city. No VPN required.
Business continuity
On-premise: if the PBX hardware fails, your phones stop. If the office floods, burns, or loses power, no one can make or receive calls — and those calls are not automatically redirected anywhere. Disaster recovery requires advance planning and often additional hardware.
Hosted: the phones follow the people, not the building. Staff can take calls on their mobiles or laptops from any location. Geographic independence is built in by default, not bolted on afterwards.
The PSTN switch-off: a deadline that changes everything
If you are running an on-premise PBX connected to ISDN lines, there is a hard deadline you need to know about.
BT Openreach is switching off the PSTN (Public Switched Telephone Network) — including ISDN — in January 2027. After that date, ISDN lines will stop working. Any PBX that depends on ISDN connectivity will be dead.
This is forcing a migration decision for thousands of UK businesses. You can either invest in upgrading your on-premise system to SIP trunking (more hardware, more cost, more complexity), or you can use this moment as the trigger to move to hosted VoIP and be done with it.
The switch-off does not affect hosted VoIP providers — we already run on modern IP infrastructure.
When on-premise PBX still makes sense
It would be dishonest to say on-premise is never the right answer. There are scenarios where it remains defensible:
- Very large enterprises — 500 or more users — with a dedicated internal telecoms team and the resource to manage a complex system properly.
- Specific regulatory environments where call data must not leave a physically controlled on-site location.
- Already fully depreciated systems with no ISDN dependency, where the hardware is running well and a migration creates more disruption than benefit.
If you do not recognise your business in that list, you are probably not in the on-premise camp.
For UK SMBs, hosted wins
For small and mid-size UK businesses — and that covers the vast majority of companies — hosted VoIP delivers lower total cost, faster deployment, easier scaling, better remote working support, and stronger business continuity. The maintenance burden disappears. The upfront hardware cost disappears. And the January 2027 PSTN switch-off does not become your emergency.
VoIPninjas is a fully hosted provider. We run our own UK infrastructure. There is no on-premise component, no hardware to ship, and no engineer to wait for. You can be live within 10 working days of signing up, on a 28-day rolling plan with no long-term contract.
Ready to move away from on-premise? Try VoIPninjas free for 14 days — no card required, no commitment. Plans start from £5.99 per user per month. Get started today.
Frequently asked questions
Can I keep my existing phone numbers if I switch to hosted VoIP?
Yes. Number porting allows you to bring your existing business numbers across to a hosted VoIP system. At VoIPninjas, we handle the porting process for you. In the meantime, your calls keep working on your current numbers.
How good does my internet connection need to be?
VoIP calls use roughly 100 kbps per concurrent call. A standard business broadband connection handles this comfortably for most teams. If you are running 20 or more simultaneous calls, we can advise on whether your current connection is adequate — call us on 0330 043 2388.
What happens to my phones if the internet goes down?
Hosted VoIP does depend on an internet connection. If your office internet goes down, calls can automatically fail over to mobile numbers. Most businesses treat this the same way they treat any other internet outage — with a backup 4G router or a mobile failover rule. We can walk you through the options.
Is hosted VoIP secure?
Yes, when it is configured correctly and run on properly maintained infrastructure. VoIPninjas uses encrypted SIP (TLS) and encrypted media (SRTP) across our network. Our infrastructure is UK-based and monitored around the clock. We do not share infrastructure with consumer services.