This blog was originally published by Sereno IT Support here

PSTN Switch-Off: Why UK Businesses Need to Move to VoIP Now

The UK’s old PSTN phone network is being switched off, and businesses still relying on it risk losing the ability to make and receive calls. Here’s why VoIP is the answer, and how to migrate smoothly.

Technology keeps moving quickly, and every major change brings a mix of benefits and disruption. One of the biggest changes now facing UK businesses is BT’s permanent retirement of the Public Switched Telephone Network, or PSTN.

“What exactly is PSTN, and why should I care?” you might ask. In simple terms, PSTN is the traditional infrastructure behind landline calling. It is the older generation of business telephony, built on analogue technology and a physical network of copper cabling used to carry voice traffic. If you remember picking up a handset and hearing a dial tone, that is PSTN at work.

Its shutdown has direct consequences for your business. If you still depend on PSTN, you face losing the ability to make and receive calls, use fax services and, in some cases, maintain internet connectivity. The practical point is simple: if PSTN still underpins part of your communications, you need to move away from it before it affects business continuity.

How do I know if I’m using PSTN?

Before you move to an alternative, you first need to understand where PSTN (Public Switched Telephone Network) is still being used. It is not limited to standard office phones. Door-entry systems, CCTV networks, fax machines, PSTN alarm systems and EPOS systems can also depend on it, although here we are focusing specifically on telephony.

Knowing what you currently rely on shapes the entire migration plan. These are some of the clearest signs that PSTN is still part of your setup:

1. Analogue phones, traditional handsets connected to wall sockets and using landline numbers.
2. Fax machines, if you still use a traditional fax machine, PSTN is involved.
3. ISDN services. Integrated Services Digital Network lines are commonly linked with PSTN infrastructure.
4. DSL internet. DSL broadband often uses the same physical network as PSTN.
5. Dial-up modems, a strong indication that PSTN is still in use.
6. Traditional phone bills, ongoing charges for fixed telephone lines usually point to PSTN.
7. Consult your provider, they can confirm exactly what technology your services are running on.

I’m using PSTN, what do I do?

As the PSTN switch-off moves further into its critical phase and ‘stop sell’ rules are enforced across the UK, the issue is no longer simply about replacing ageing technology. It is about making sure your business can continue communicating without interruption.

The safest approach is to move to digital telecommunications as soon as possible. At Sereno, our recommendation is clear: transition to Business VoIP without delay.

VoIP (Voice over Internet Protocol) is a form of digital communication that carries voice calls across your broadband connection instead of traditional telephone lines. That removes the restrictions associated with fixed landlines and gives your business far more flexibility in how it communicates.

Why business VoIP?

Internet calls, video conferencing, and online collaborative tools have far exceeded the capabilities of PSTN, and it is becoming increasingly difficult to maintain. By the end of 2025 PSTN will be switched off across the United Kingdom, ushering in a new era of telecoms.

— BT, on the UK PSTN switch-off

Editor’s note: BT have since rescheduled the PSTN switch-off to January 2027.

BT summed up the situation well. With the deadline approaching, it makes sense for UK businesses to make the switch to business VoIP now rather than leave the change until the last minute. Moving earlier gives you more time to plan properly and reduces the risk of disruption as the shutdown gets closer.

There is also a stronger business case beyond the deadline itself. VoIP is more capable and more cost-effective than traditional landlines. It gives you greater functionality, simpler scalability and improved cost-efficiency, while supporting the way modern teams actually work, including hybrid working across different locations.

VoIP vs PSTN, how do they compare?

VoIP is typically more adaptable, more economical and easier to manage than PSTN. That is why so many UK businesses have already moved away from traditional landlines.

Here is how the two approaches compare:

How does business VoIP work?

VoIP connects calls through the internet, so your employees can make and receive calls using a computer, a dedicated VoIP handset or a conventional phone connected through an appropriate adapter.

Using a computer means your staff can simply sign in and begin working without needing an additional device. That works particularly well for employees splitting their time between home and the office. Calls can also be made while travelling using wireless hotspots or 4G/5G connectivity.

If you decide to switch, the first step is choosing a VoIP provider and a package that matches your business requirements, including the number of people who need to make calls. We can help you work that out.

You then receive the required hardware and software, including VoIP phones and servers, while your provider takes responsibility for configuring and maintaining the system.

Ready to switch to business VoIP?

You now know why PSTN is being retired and why VoIP is the stronger alternative. Before making the move, there are several things you need to consider before, during and after migration.

1. Before, prepare for the switch

Start by checking that your internet connection has sufficient bandwidth for the number of calls your business makes. The bandwidth required for each call is very small, so most providers can support it without difficulty, but it is still worth checking.

Best practice is to run VoIP across a secondary internet connection so that telephony can continue if your primary line fails. Some providers offer a lower-cost ‘Assured IP line’ designed specifically for voice traffic.

You should also confirm whether your current handsets support VoIP, because many traditional phones do not. Decide whether your users need desktop applications, mobile applications or both, and identify the features you actually require, such as menu systems, voicemail, call recording, call statistics and reporting.

2. During, make the move

Your VoIP provider and/or IT partner should support you throughout the migration.

A sensible approach is to test the new service alongside your existing telephone system using separate numbers before moving your main numbers across. We recommend asking for free demonstrations of cloud-based VoIP platforms and testing them properly before committing.

You should also document your current telecoms setup clearly, including menu structures, hunt groups, call trip-overs and direct dial numbers.

Number porting can take time, so make sure your provider gives you a clear timeline before the migration begins.

3. After, bed it in

Continue testing once the system is live and ask staff to log any issues they encounter.

When changes are made to your setup or call flow, update your documentation so that the final configuration is clearly recorded.

Switch to VoIP with Sereno

The simplest way to choose between UK VoIP providers is to work with your IT partner.

At Sereno, we help you identify the right provider and package while acting as your single point of contact, so your telephony and wider technical support sit under one roof.

With Sereno you’ll benefit from:

• The support service you expect, with consistent, agreed SLAs in line with the rest of your IT support
• A dedicated team of IT experts who liaise with your VoIP provider for you, so you’re never stuck in the middle
• Confidence that the network infrastructure VoIP relies on is already managed by us
• Help with the installation process, set up in a reliable way that’s easy for us to support
• Transparent advice about the best VoIP providers and plans for your business
• More competitive pricing, thanks to our long-standing, trusted relationships with world-class suppliers

For more information, contact us today and speak to an IT advisor about how Sereno can help you switch to business VoIP.