What is being switched off?
Openreach is retiring the Public Switched Telephone Network (PSTN) and ISDN, the copper-based services the UK has used for decades. That includes standard analogue lines, ISDN2 and ISDN30, and services built on them such as BT Featureline. After 31 January 2027, calls will need to run over the internet instead. Read our PSTN switch-off guide for the key dates.
Your options
| Option | Best for | What changes |
|---|---|---|
| Hosted VoIP (for example 3CX) | Most small and medium businesses | Your phone system moves to the cloud. Calls work on desk phones, computers and mobiles. |
| SIP trunks | Businesses with a newer on-site phone system | Your existing system stays, but connects over the internet instead of ISDN. |
| Microsoft Teams calling | Teams-heavy organisations | Calls are made and received in Teams, with a calling plan or direct routing. |
For most businesses, hosted VoIP is the simplest and cheapest route. There is no phone system to maintain on site, and staff can take calls anywhere.
Step 1: audit your lines and numbers
Gather your phone bills and list every line and number, including direct dials, fax numbers and lines that seem unused. Some of those lines may be used by alarms, lifts or card machines. See our guide to alarms, lifts and card machines.
Step 2: check your internet connection
VoIP needs a stable connection. Each call uses about 0.1 Mbps in each direction, so speed is rarely the problem. Reliability and upload speed matter more. Full fibre or SOGEA broadband suits most offices, and busy sites may need a leased line. See what internet speed you need for VoIP.
Step 3: choose your system and features
Decide what you need: call queues, ring groups, call recording, voicemail to email, opening hours, mobile apps and integrations. A good provider will set these up for you, matching how your team works today.
Step 4: port your numbers
You can keep your existing numbers, including geographic numbers like 01622 and non-geographic numbers like 0333. Your new provider requests the port and agrees a date. Porting usually takes a few weeks, so start early.
Important: do not cancel your old lines before the port completes. If the line is cancelled first, the number can be lost.
Step 5: go live and tidy up
- Set up handsets and apps before the switch date.
- On port day, test inbound and outbound calls from every number.
- Move any alarms, lift phones or card machines that used the old lines.
- Only then cancel any remaining lines, and check final bills.
What does it cost?
Business VoIP typically costs between £7 and £30 per user per month. AVAIO’s 3CX system is £14 per user per month + VAT, with no contracts and no set-up fees. Business broadband starts from £25 a month and leased lines from £235. See our guide to business VoIP costs.
How AVAIO can help
We move Kent businesses from ISDN and analogue lines to VoIP every week. We audit your lines, check your broadband, port your numbers and set up your system, with a local team on hand if anything needs attention. Telecoms clients save 36% on average.