The big public switched telephone network (PSTN) switch-off is imminent. As 2025 ends, this system – which is operated by BT – will be turned off forever.
The UK’s PSTN has been with us since 1876, routing phone calls to and from phones all over the country, using millions of miles of network cable. But there are now more efficient systems available, which is why the switch-off is happening.
In some countries, it’s already happened. The Netherlands and Estonia, for instance, have already seen PSTN lines phased out. Others, including Japan, Germany and Australia, have set dates for their own PSTN line switch-offs.
This means that individuals and businesses using PSTN-based telephony will need to upgrade their set-up to ensure they can continue communicating.
So, what options are available if you need to migrate before the PSTN switch off?
The alternative is hosted VoIP (voice over internet protocol): a digital service that allows users to make voice calls using a connected device via the internet.
In this guide, we’ll explain:
- How PSTN works
- How PSTN and ISDN differ
- Why they’re both being switched off
- The technology that’ll replace it
- What you can do to get ready
If you still have questions afterwards, why not contact our team for further guidance?
What does PSTN stand for and mean?
PSTN is short for public switched telephone network. It’s a global system of telephone networks that use copper wires to transmit analogue voice data. But the equipment used to run it is old and expensive to maintain. That’s why providers like BT are investing in digital technology designed to better meet the needs of their customers.
But just what is a PSTN phone line?
PSTN phone lines are made of copper. They connect most UK homes and offices to cabinets on the street, which are then connected to local telephone exchanges.
It’s important to note that PSTN lines are dedicated. As a result, people can only use a PSTN phone line for one purpose at a time. This is why, in the early days of the internet in the 90s, households couldn’t use the internet and their landline phone at the same time.
How do PSTN phone lines work?
This is how the UK’s current system of PSTN lines works:
- You pick the phone up and dial a number
- A dedicated circuit is created between your phone and the phone you’re calling
- When you speak, the sound waves are converted into electric signals
- These signals are transported through telegraph lines (distribution points) to street cabinets (or primary connection points)
- From there, the signals go to the telephone exchange (also known as a central office, switching office or network tandem)
- Those signals are then relayed to the phone you’re calling and are converted back to sound waves
The rate of data transmission over PSTN lines is influenced by various factors, including the type of copper wire, distance covered and external conditions.
The electromagnetic properties of copper can also interfere with the speed of transmission. As these phone lines were usually laid underground next to electrical cables, electromagnetic fields can occur and affect phone signals.
What are PSTN lines used for?
The main function of PSTN lines in the UK has been to connect phone calls. However, some other technologies also use the PSTN system and will need to be reconfigured after the PSTN switch-off. These include:
- Fax machines
- Electronic point of sale machines
- Alarm systems for houses and businesses
- CCTV
- Door entry systems
What are the benefits of PSTN?
The PSTN system has served us well, particularly in places like the UK, where it’s been in use for over 150 years. There are several advantages that have contributed to its longevity:
- Reliability – PSTN lines are generally stable, with voice distortion or call dropout rarely occurring
- Security – dedicated lines make PSTN systems highly secure
- Low maintenance – while business lines or a private branch exchange (PBX) cost more in upkeep, residential PSTN lines need very little maintenance. This is one reason the system has endured so long.
- Always on – as the power supply is fed directly over the phone line from the exchange, it’s not affected by the building’s electricity supply
Ultimately, however, PSTN is an outdated system, overtaken by the digital world and new ways of living and working.
What are the disadvantages of using PSTN?
PSTN has been a trusty servant, but governments around the globe now recognise its time has come. In today’s world, holding onto a PSTN system would have various disadvantages:
- Expensive set-up – between £6,000 and £10,000 for a 30-person business
- Expensive calls – costly international and mobiles, compared to free VoIP-to-VoIP calls
- Higher monthly costs – it can cost up to £50 per user each month
- Integration – PSTN offers no possibility for software integration
- Difficult to scale – extra hardware makes scaling up complex and costly
- Outdated – PSTN is not supported over the internet
What is a PSTN line fault?
Typically, a PSTN line fault occurs when the PSTN line fails to transmit the connection signal from its point of origin to its intended destination, or when the digital signal quality deteriorates.
This scenario is becoming more and more common since the lines are now so old. In some cases, the copper wires are suffering corrosion after the protective rubber covering has degraded over time.
Whatever the cause, more frequent faults are resulting in more unpredictable service, higher maintenance costs and greater repair costs. The case for switching off PSTN is becoming more and more compelling.
What is the difference between PSTN and ISDN?
ISDN stands for integrated services digital network and has (alongside PSTN) been the primary form of communication for decades. PSTN uses a single line, while ISDN supports up to 30 lines over a digital transmission connection of up to 2Mbps.
This is how ISDN enables you to manage multiple calls across the same line at once, ideal if multiple people are on the phone in the same office. PSTN lines, however, don’t – and that’s a problem if you run a business. If customers can’t get through, they’ll give up and go elsewhere.
Although ISDN uses the PSTN network to operate, it’s completely digital. This means it can provide multiple lines and a host of other useful features, which can be scaled quickly, resulting in superior call quality and video. This makes it much easier and faster than old PSTN set-ups, where each line needs to be physically plugged in. So you may be surprised to hear ISDN is also nearing the end of its lifespan.
Why is ISDN being abolished? Like PSTN, it transmits data using copper wires that are expensive to maintain. This cost is then passed on to customers in the form of prohibitively expensive line rental packages.
What is the 2025 PSTN switch-off?
The PSTN switch off will happen in December 2025, but new orders will be stopped from two years prior. BT owns the service, which includes various Wholesale Line Rental (WLR) and ISDN products. These products are purchased by Communication Providers (CPs) who sell them under their own branding at regulated prices.
Here are the key points to remember:
1. The PSTN switch off will also affect ISDN lines. However, businesses can still purchase ISDN lines until 2023. But providers are encouraging their customers to invest in newer technologies instead - because purchasing ISDN equipment will become harder and support for it will rapidly decrease.
2. PSTN and ISDN are being replaced by fast fibre broadband. The cost of maintaining these seldom-used systems makes little sense when providers could use that money to invest in a faster and more efficient infrastructure that provides a better service for end-users.
3. The PSTN switch off is imminent. This means individuals and businesses using outdated legacy systems should speak to their providers and seek advice about the next best steps if they’re to avoid costly disruption and to keep up with competitors.
4. Phase one will occur in September 2023 when BT stops selling Wholesale Line Rental (WLR). WLR is a service that lets a Communication Provider (CP) use an operator’s service and sell it under its own branding. Finally, in December 2025, PSTN and ISDN will be switched off permanently.
What will replace PSTN?
The UK government has a target of equipping every home with gigabit broadband by 2030. By the time of the PSTN switch-off in December 2025, the government is aiming for 85% full-fibre coverage. Although there is still work to do, expect IP-driven services like VoIP to become the norm soon.
Our fast fibre future will see us communicate using internet-driven services like voice over internet protocol (VoIP). Also known as IP technology, VoIP doesn’t require a circuit-switched network. Instead, it sends voice data in chunks or packets, which makes it faster than the PSTN.
In addition, VoIP offers advanced, in-built features such as call forwarding, call waiting, caller ID, conference calling and voicemail.
PSTN vs. VoIP
Compared to PSTN, VoIP is cheaper, offers unlimited scalability, can be tailored to the needs of subscribers, and removes the need to change numbers when a business moves premises. Here are some of the biggest differences between the systems:
Price
Set-up and monthly costs are cheaper with VoIP. Plus, VoIP-to-VoIP calls are free.
Security
With VoIP, how secure your system is depends on the security of your internet connection. PSTN lines are extremely secure because they’re dedicated.
Scalability
Increasing the number of users is simple with VoIP. You can even do it instantly, in many cases. Extra hardware is required for upscaling PSTN lines.
Features
VoIP gives you more in-built features, including video calling, voicemail, click-to-call services on websites, recording services, messaging and presence information.
Power
Traditional corded landline phones – using PSTN – will work during a power outage, while VoIP relies upon an internet connection and won’t work.
What are the benefits of the PSTN switch-off?
The benefits of the switch-off are clear to see:
- No more time or money spent supporting an outdated system
- Opportunity to replace PSTN with a more modern, efficient system
- Businesses get a future-proofed, scalable solution instead
- Better integration will improve productivity
- Everyday costs will fall
- Voice calls are available over any device
How can your business prepare for the PSTN switch-off?
One thing is for certain: the PSTN and ISDN switch off will happen in December 2025 and the impact on unprepared businesses will be extensive.
If you rely on either or both of these legacy systems, you’ll need to take steps to prepare your business and avoid costly and disruptive problems later.
Here are three initial steps you can take:
1. Audit your telephony estate
Which (if any) areas of your business use PSTN or ISDN? This is especially important for businesses operating across multiple sites. Some premises may use fast fibre broadband - while others still rely on PSTN or ISDN technology.
Auditing your infrastructure will give you the bigger picture. When running your checks, don’t forget to include other systems, like alarms, which may also rely on PSTN or ISDN to function.
Finally, consider whether these systems can be adapted or need to be replaced entirely. Your provider will be able to help with these questions.
2. Check your internet speed
Even if your system is up-to-date, is it good enough? Fast fibre broadband is becoming the go-to choice for businesses worldwide which means investing in the latest technology is essential unless you want to fall behind your competitors. Additionally, cost of fibre services are largely competitive now, meaning your business could benefit from better performance for nearly the same rate.
3. Create a plan - check it often
It may not seem it, but December 2025 is imminent. Setting a plan in motion now will help you get ready for the PSTN switch off and avoid surprises. That doesn’t mean things are set in stone. Watch developments and adapt your plan to reflect changes before committing to a strategic decision.
4. Exploring the market
There are a variety of providers who can support you throughout this migration and help you select the best solution for your needs. The research and implementation process can take some time, so it’s worth starting this process well ahead of time to avoid any unnessecary business disruption.
Working with an experienced fibre network specialist will help ensure you make the right choices. Connect with one of our knowledgeable experts to discuss your circumstances so we can find a solution that best suits your needs.
How can we help?
We’re focused on ensuring our customers have the connectivity their business needs. Whether it’s Dark Fibre, Dedicated Internet Access or Ethernet, we’ll find a tailored solution that offers you a reliable, smooth internet connection. We’ll make sure you’re thoroughly prepared for the PSTN switch-off, giving you a cost-effective service that supports VoIP and more integrated communications technology.
