PSTN/ISDN Switch-Off 2027: What UK SMBs Must Do Now

The ISDN switch-off UK 2027 deadline is coming fast. In January 2027, BT will permanently shut down the UK's Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN). If your business still uses traditional phone lines, you've got less than nine months to act.

What the PSTN ISDN switch-off means for your business

This isn't just about your phones. The switch-off affects every piece of equipment that connects through traditional copper phone lines.

Your business phone system will stop working completely. No dial tone. No incoming calls. No fax machines. If you've got card payment terminals connected through phone lines, they'll go dead too.

Alarm systems that use phone lines to call monitoring centres will fail. Door entry systems, lift emergency phones, and fire safety equipment all rely on these old networks.

You can't just wait and see what happens. Once January 2027 hits, there's no going back. BT isn't offering extensions or grace periods.

Why the switchover is happening now

BT's copper network is over 100 years old. The equipment is increasingly unreliable and expensive to maintain. Parts are getting harder to find. Engineers with the skills to fix PSTN equipment are retiring faster than they can be replaced.

The future is IP-based communication. Voice over Internet Protocol (VoIP) offers better call quality, more features, and lower running costs. But it needs proper network infrastructure to work reliably.

Openreach has been rolling out fibre broadband across the UK to support this transition. Most areas now have access to high-speed internet connections that can handle business phone systems.

Step 1: Audit your current phone and data setup

Start by listing everything in your business that uses a phone line. Don't just think about handsets on desks.

Check your payment terminals. Most older card machines connect through phone lines. Your merchant services provider needs to know about the switch-off.

Look at your security systems. Burglar alarms, CCTV systems, and access control often use phone lines for remote monitoring.

Find your lift maintenance contract. Emergency phones in lifts typically connect through PSTN lines. Your lift company will need to upgrade these.

Check any fax machines you still use. Yes, some businesses still need fax for legal or compliance reasons. You'll need a fax-to-email service or IP fax solution.

Step 2: Test your internet connection for VoIP readiness

VoIP phone systems need reliable internet connections. Your current broadband might not be up to the job.

Run a speed test during your busiest hours. You need at least 100kbps upload and download speed per concurrent call. So if you've got 10 people on calls at once, you need 1Mbps dedicated to phones.

Check for packet loss and jitter. These cause poor call quality - voices cutting out, echoes, delays. A standard broadband speed test won't show these problems.

Consider a dedicated internet connection for your phones. Shared connections struggle when someone's downloading large files or streaming video during important calls.

Your network infrastructure matters too. Old switches and routers might not handle VoIP traffic properly. Cat5e cabling should work fine, but Cat6 is better for future-proofing.

Step 3: Choose your PSTN replacement solution

You've got several options for replacing your PSTN phone system.

Hosted VoIP is the most popular choice for SMBs. Your phone system runs in the cloud. You just need IP phones and a good internet connection. Monthly costs are predictable and you get enterprise features without the upfront investment.

On-premise IP PBX gives you more control. The phone system hardware sits in your office. Higher upfront costs but lower monthly fees. Good if you've got specific integration requirements or security concerns.

SIP trunking works if you want to keep your existing phone system. You replace the phone lines with internet-based connections. Only viable if your current system supports SIP and is worth keeping.

Mobile-first solutions suit businesses where staff are rarely at desks. Calls come through smartphone apps. Works well for field service companies or consultancies.

Step 4: Plan for business continuity during the changeover

Switching phone systems can disrupt your business if not planned properly. You can't afford to be unreachable during the transition.

Schedule the changeover outside business hours. Weekend installations work best. If that's not possible, plan the work for your quietest day.

Set up call forwarding to mobile numbers as a backup. If something goes wrong with the new system, calls can still reach your team.

Test everything before going live. Make test calls to and from the new system. Check voicemail, call forwarding, and any integrations with your CRM or helpdesk software.

Train your staff before the switch. VoIP phones have different features from traditional handsets. Show people how to transfer calls, set up voicemail, and use any new features you're adding.

Keep your old system running in parallel for a few days if possible. This gives you a fallback option if problems emerge.

Common mistakes to avoid during your PSTN migration

Don't assume your internet connection can handle phone calls just because web browsing works fine. Voice traffic has different requirements from data.

Don't forget about number portability. You can keep your existing phone numbers when switching to VoIP, but the process takes time. Start the porting process early.

Don't ignore your existing cabling infrastructure. VoIP phones need network connections, not phone sockets. You might need additional Ethernet points or wireless coverage.

Don't leave emergency systems until last. Fire alarms, lift phones, and security systems often have specific requirements and longer lead times for upgrades.

Don't assume all VoIP providers are the same. Check their UK presence, support hours, and service level agreements. Cheap isn't always best when it comes to business communications.

How TechCare Networks helps with your PSTN replacement

We've helped hundreds of UK SMBs prepare for the ISDN switch-off. Our approach starts with understanding how your business actually uses phones and data.

Our free site survey identifies everything that needs upgrading. We test your internet connection for VoIP readiness and check your network infrastructure. You get a detailed report showing exactly what needs to change.

We handle the technical side so you can focus on running your business. That includes liaising with your VoIP provider, configuring network equipment, and installing any additional cabling you need.

Our structured cabling work meets all current standards. Cat6A cable installation supports current VoIP needs and future requirements like Wi-Fi 7 access points.

We offer ongoing managed services to keep your new setup running smoothly. Remote monitoring catches problems before they affect your business. UK-based support means you can speak to someone who understands your local requirements.

Frequently asked questions

Below are answers to common questions about the PSTN ISDN switch-off and what UK businesses need to do.

When exactly does the PSTN ISDN switch-off happen in the UK?

The final switch-off date is January 2027. BT will permanently shut down all PSTN and ISDN services across the UK. There are no regional variations or extensions to this deadline. If your business still uses traditional phone lines after this date, your phones will simply stop working.

Can I keep my existing phone numbers when switching to VoIP?

Yes, you can port your existing business phone numbers to a VoIP system. The process typically takes 10-15 working days and must be arranged through your new VoIP provider. Start the porting process early as there can be delays, especially for businesses with multiple numbers or special number types.

What internet speed do I need for VoIP phones?

You need at least 100kbps upload and download speed per concurrent call. A business with 10 staff making calls simultaneously needs 1Mbps dedicated to phones. However, connection quality matters more than raw speed. Packet loss and jitter cause poor call quality even on fast connections.

Do I need to upgrade my network cabling for VoIP?

Existing Cat5e cabling will support VoIP phones, but you might need additional network points. VoIP phones connect to your network switch, not traditional phone sockets. Many businesses need extra Ethernet outlets installed or Power over Ethernet capability added to power desk phones through the network cable.

What happens to my alarm system after the PSTN switch-off?

Alarm systems that use phone lines for monitoring will stop working in January 2027. You'll need to upgrade to IP-based monitoring or cellular backup options. Contact your alarm monitoring company now as they may need to replace equipment and test new connections before the deadline.