How to switch your business phones to VoIP (step-by-step)

What does switching to VoIP actually involve?

Switching to VoIP means moving your calls from the old copper phone network onto your internet connection. Instead of a dedicated line, calls travel as data, and your phone system lives in the cloud. There is no on-site switchboard to install and no engineer needs to dig anything up.

In practice you do three things: recreate how your calls are handled today, move your numbers across, and put the right app or phone in front of each person. The provider does most of the technical work, including the number port. If VoIP is new to you, our explainer on what VoIP is and how it works gives the background in plain terms.

The reason this matters now is the 2027 switch-off. The UK PSTN and ISDN networks close on 31 January 2027, so every business has to make this move at some point. Our guide to the 2027 PSTN and ISDN switch-off covers the deadline and the wider checklist for connected devices like alarms and lifts. Doing it now, calmly and in your own time, beats doing it under pressure.

How do I switch to VoIP? The step-by-step process

Here is the full process from start to finish. Work through it in order and the switch is low-risk, with your old lines acting as a safety net until the new system is proven.

1. Audit your current phone setup. List your numbers, lines, handsets, how calls are routed today and anything else plugged into a phone socket. This tells you what to recreate and what to port.
2. Check your broadband. Confirm your internet can carry calls. Each VoIP call uses about 100 kbps each way, so most business broadband is fine. A full-fibre FTTP or SoGEA line is ideal. Order an upgrade if needed.
3. Choose a provider and plan. Pick a UK hosted VoIP provider that includes UK calls, number porting, mobile and web apps, desk phone support and the call handling you need, then size the plan to your user count.
4. Order numbers and port existing ones. Order any new numbers and ask the provider to port your existing business numbers. You keep the same numbers and the provider runs the port, so you do not cancel your old line first.
5. Set up users and call routing. Create each user, install the mobile and desktop apps, set up your auto-attendant menu, ring groups, business-hours routing and voicemail-to-email to match how you want calls handled.
6. Test in parallel. Run the VoIP system alongside your old lines. Make test calls in and out, check the menu, transfers, voicemail and call quality, and fix anything before you rely on it.
7. Go live and cancel the old lines. Switch calls to the VoIP system on the agreed port date, confirm everything works, then cancel the old PSTN or ISDN lines so you stop paying for them.

How long does switching take and is there downtime?

For most small and medium businesses the hands-on setup is quick. Creating users, installing apps and building your call menu can be done in a day. The clock that everyone watches is number porting, because the calendar date when your numbers move is set in advance with both providers.

Task	Typical timescale
Account and user setup	Same day
Installing apps and desk phones	Same day to a few days
Building call routing and menus	Same day
Porting a single geographic number	A few working days
Porting larger or non-geographic ranges	Up to around two weeks

There should be no downtime if you do it right. Because the VoIP system runs in parallel with your old lines, you test everything before anything changes for callers. On the agreed port date the numbers move across and calls start arriving on the new system. Customers keep dialling the same numbers and never see the change. Our guide on keeping your number when switching to VoIP explains porting in more detail.

What do I need before I switch?

You need surprisingly little. The two essentials are a decent internet connection and a list of how your calls work today. Everything else the provider supplies.

On internet, the bar is low for voice itself. A single call uses roughly 100 kbps each way, so even a ten-person office juggling several simultaneous calls needs only a few Mbps set aside for voice. Most business broadband manages this comfortably alongside normal web use. A full-fibre connection gives the most consistent quality, and a router that can prioritise voice traffic helps if your line is busy. Our guide on what internet speed you need for VoIP has the bandwidth figures by team size.

On hardware, you do not have to buy new phones. Staff can take calls through a mobile app, a web softphone in the browser, or a VoIP desk phone, and many teams mix all three. People who are out and about use the mobile app, office staff use a browser or a handset. This flexibility is one of the main reasons businesses prefer VoIP to a fixed landline.

What can go wrong, and how do I avoid it?

The switch is low-risk, but a few simple checks remove the common pitfalls. None of these are hard, they just need to be done before go-live rather than after.

The first is forgetting connected devices. Alarms, lift phones and old card machines may rely on the line you are about to cancel. Audit these early and arrange IP or mobile replacements, because some have long lead times. The second is rushing the port. Agree the port date in advance, keep the old line until the port completes, and do not cancel anything until the new system has handled real calls.

The third is skipping the test phase. Make genuine test calls in and out, walk through your auto-attendant menu, try a transfer and leave a voicemail, and listen for call quality. If quality is poor, it is almost always the local network rather than VoIP itself, and prioritising voice on the router usually fixes it. Browse more practical guides on our Learn hub if you want to dig into any single step.