Summary of the main issues

There’s more information about what is changing, why, and when in the rest of the guidance below, but at high level the summary here sets out the main issues.

The traditional analogue phone network (or ‘PSTN’) will reach ‘end of life’ by December 2025, being replaced by digital technologies.

As part of this program, new PSTN and ISDN lines will not be available beyond September 2023.

All existing ISDN and PSTN lines will then be withdrawn by December 2025:

  • This means that any ‘traditional’ phones and phones systems will not work by 2026 and will need to be changed.
  • It also means the connectivity (i.e., broadband) products that use the PSTN will have to be changed for 2026 too.

Boxes showing 2022 to 2026 and what is happening

Summary of solutions

The detail in the rest of this guidance covers particular points and questions, however the summary below may be useful in quickly determining what needs to be done.

For telephony

By 2026 all calls will be made and received over the internet.

In the domestic market (i.e., residential premises), the existing service providers will be offering ‘VoIP’ services to deliver telephony over the new data-only connections.

For businesses, those with legacy telephone systems (i.e., using PSTN or ISDN lines) will need to take action, but there is an opportunity to save money and greatly enhance functionality with a VoIP telephone system.

For connectivity

By 2026 all connectivity using the PSTN will need to be replaced with alternatives.

This is important; there are numerous organisations pointing out the telephony issues that the PSTN switch off will give rise to, but far fewer describing the impact on broadband services.

Because of the way the services are constructed, Virgin Media, ‘alt-net’ and mobile phone services (see ‘who provides the telephone and broadband services?’ below for more info) are much less likely to be affected, and ‘FttP’ or ‘full-fibre’ services (including ‘leased lines’ for businesses) are fine too.

Broadband services like ‘ADSL’ and ‘FttC’ (see ‘what do the different broadband and connectivity technologies mean?’ below for more details), however, will need to be replaced with newer technologies.

Openreach products are being released that allow broadband services to be provided that are similar the current ones, but aren’t PSTN-based: look out for ‘Single Order’ (or ‘SO’) products.

Background: what do all the terms and acronyms mean?

Telephony, connectivity, voice, data: all of these, and many more, are technical or technological concepts and inevitably there are a number of different terms and acronyms used.


Telephony is a general term used to mean the telecommunications services (where ‘tele’ comes from the Greek word for ‘far’) that allow electronic communications over distance.


The term ‘voice’, which generally means the same as ‘telephony’, is used to similarly describe those same telecommunications services, and helps to distinguish between the other common use of networks today, that being to allow electronic transmission of ‘data’.


Connectivity is a general term often used to refer in non-specific terms to the range of technologies that may be used in creating network connections.


In this context, the term ‘data’ is used to distinguish between ‘voice’ and all the other information that moves across a network (like web pages, emails etc.)


PSTN stands for Public Switched Telephone Network, which provides infrastructure and services for public telecommunications. Originally using fixed-line analogue systems, the PSTN core network is now digital, while the ‘edge’ (the bits that connect to local premises) is still often analogue.

A standard analogue telephone line, often presented in a white box on the wall, is referred to as a ‘PSTN line’.


DSL stands for Digital Subscriber Line, a technology used to transmit data over a telephone line. In the late 1990s DSL deployment accelerated, and became the primary ‘broadband’ technology for homes and small businesses in the UK.

Usually delivered in parallel to, and over the same cabling as the voice service, the underpinning DSL technology continues to power the Fibre-to-the-Cabinet (FttC) connectivity products that many homes and businesses use today.


Alongside the PSTN and DSL, is ISDN, which stands for Integrated Services Digital Network. An ISDN line is a bit like a bundle of PSTN lines, allowing several telephone calls (as many as 30 per ISDN line) to happen simultaneously.

ISDN also supports data as well as voice, but most businesses have adopted DSL for this.

Launched in 1991, there are generally two ISDN services in use today:

  • ISDN2e – supporting two simultaneous calls (and up to 0.125 Mbps for data connectivity); and
  • ISDN30 – supporting between eight and 30 simultaneous calls

Many businesses continue to use one of these ISDN services to connect legacy telephone systems.


VoIP stands for ‘Voice over Internet Protocol’, and this means using an internet connection (designed primarily for data, and running on Internet Protocol, or ‘IP’) to carry voice from source to destination.

VoIP supports phone calls with all the features of traditional analogue telephone systems (including things like voicemail, call forwarding, and caller ID).


SIP stands for ‘Session Initiation Protocol’, which is used to allow voice to be run over data networks that use Internet Protocol. SIP is a signalling protocol, replacing the analogue signalling on the PSTN, that sets up, controls and ends communication sessions (e.g., phone calls).

Single Order

Single Order or ‘SO’ products are Openreach variants that are ‘data only’ broadband services; they don’t use the PSTN, and don’t include a voice service as standard as a standard PSTN telephone line does. SO products include:

  • SOGEA: Single Order Generic Ethernet Access, the Openreach broadband only replacement for FttC, where fibre connects the exchange and the street cabinet, and copper connects the street cabinet and the local premises (i.e., the home or the office); and
  • SOTAP: Single Order Transition Access Product, the Openreach broadband only replacement for ADSL, for areas where there is no fibre connection to the street cabinet.

The SO product provides comparable performance to its PSTN-based predecessor (e.g., for a given location, SOGEA will provide the same speed as FttC).

Background: what do the different broadband and connectivity technologies mean?

Connectivity is based on telecommunications company (or ‘telco’) infrastructure: wires (which may be metallic or fibre-optic), or waves (e.g., radio or microwave) between two points making a connection.

Each connection passes data in both directions; data passing ‘down’ from somewhere else (e.g., the internet) is referred to as ‘downstream’, and data passing ‘up’ from the local point (e.g., a home, or office premises) is referred to as ‘upstream’.

Some connectivity technologies are ‘symmetric’, meaning that the speed of the connection is the same in both directions (downstream and upstream); others are ‘asymmetric’, where the downstream speed is higher than the upstream.

The speed (or ‘bandwidth’) is measured in megabits per second (Mbps). The higher the Mbps, the faster the connection.

Connectivity (including ‘broadband’) can make use of a range of different underpinning technologies.

Budget and bandwidth requirement influence the choice of technology, but geographic location and the relative performance are also key factors.

Some technologies have variable performance (i.e., the performance of the technology will vary from location to location) at a fixed charge, while others provide static performance at a variable charge (i.e., the charges for the connection will vary from location to location).


Asymmetric Digital Subscriber Line (ADSL) is basically ‘traditional’ or ‘standard’ broadband, run over a phone (or PSTN) line.

It is available in different variants, and performance is up to approx. 20 Mbps downstream and 1 Mbps upstream. It is a ‘rate adaptive’ technology, meaning that the performance is not always constant, and varies with distance and cable quality.


Fibre-to-the-Cabinet, often referred to as ‘superfast broadband’, is a variation of DSL technology where fibre is used to connect the telephone exchange and the local street cabinet, with the final connection to the premises made with a standard telephone line.

There are two main variants, offering up to 40 Mbps downstream and 10 Mbps upstream, or up to 80 Mbps downstream and 20 Mbps upstream.


The latest DSL-based technology, G.Fast moves on from FttC and can theoretically support up to 1,000 Mbps downstream (though only over very short distances).

Like FttC, the final connection to the premises uses a copper cable, and there are two main variants: up to 160 Mbps downstream and 30 Mbps upstream, and up to 330 Mbps downstream and 50 Mbps upstream.


In this sense, ‘cable’ is a term describing the connection, rather than the fact that the connection uses a cable (which it could be said that all non-wireless connections do).

Most commonly used for domestic connections, rather than for business, cable in the UK uses fibre-optic cables and, for the connection to the premises, co-axial cables (in what’s called the ‘DOCSIS 3.1’ standard) to provide high-speed connectivity and TV services. Performance downstream is typically between 100 Mbps and 1 Gbps.


Fibre-to-the-Premise, unlike the technologies above, uses fibre optic cabling instead of metallic cabling FttP all the way from the network core to the premises. This is generally regarded as a more future-proofed approach, and tends to be the technology referred to for ‘gigabit-capable’ connectivity (i.e., 1,000 Mbps).

It often shares the same core networks as solutions like FttC and G.Fast, but by pushing the fibre right the way to the local premises, can support higher speeds, though in terms of the ‘products’ available using the infrastructure (commercially and technically), they are the same as G.Fast.

Leased Line

Like FttP, the connections from the network core to the local premises are all fibre optic. Unlike FttP, however, leased lines use a more ‘dedicated’ architecture; instead of the large, shared network cores that support solutions like FttP, leased lines are supplied using specific equipment in specific locations, and are therefore more expensive.

They can support very high bandwidths (1 Gbps and more), and are usually symmetric.


Wireless technologies include point-to-point services between two premises (requiring a wired connection at the upstream premises), as well as cellular technologies (e.g., 4G and 5G) that can be used for data connections as well as in mobile phones.

Performance of wireless technologies is highly location-dependent, and can vary with weather and other factors. However, they are often one of the few realistic solutions in rural locations.

Background: who provides the telephone and broadband services?

An area that can be confusing: who actually puts the infrastructure in place that we use for telephony and data connectivity?

The actual provider is often different to the organisation that invoices for the services.

Who actually provides the networks?

A simplified answer to this is that there are basically four types of network provider in the UK:

  1. Openreach: covers almost all of the UK, and is often referred to as ‘BT Openreach’ (see below for more info about that). A wide range of organisations buy services from Openreach, using a model called Wholesale Line Rental (WLR), and then sell on, either to resellers or directly to consumers.
  2. Virgin Media: covering much of the UK, but not all, Virgin Media own and run their own network (i.e., they generally do not, though they can, buy Openreach services and sell them on). The Virgin Media network uses different technology (‘cable’) to the Openreach network.
  3. ‘Altnets’: meaning ‘alternative networks’ (as in, alternatives to Openreach and Virgin Media), these are typically ‘full-fibre’ and fully digital networks delivering high-performance connections to homes and businesses in one or more particular geographic areas.
  4. Mobile carriers: there are four major carriers in the UK (EE, O2, Three and Vodafone), with each of these also supporting a number of Mobile Virtual Network Operators (MVNOs) in a similar model to that used by alternative telecoms providers through WLR.

What is Openreach?

Openreach, referred to by some as ‘BT Openreach’, is the organisation that provides and maintains the infrastructure (cables, ducts, cabinets and exchanges) that connects most UK homes and businesses to the national broadband and telephone network.

Born within BT, Openreach was created in 2006, when BT and Ofcom agreed to a number of changes to allow competitors to BT to have access to BT’s local network. Openreach manages this local access network, connecting customers to their local telephone exchange.

In March 2017, BT plc separated Openreach further, with staff and non-network assets placed into a legally separate company, Openreach Limited. The network assets, however, remain owned by BT plc, and Openreach Limited is wholly owned by BT plc’s parent holding company, BT Group plc.

What is WLR?

Wholesale Line Rental (WLR) is a service through which an alternative telecoms operator assumes control of a telephone line from Openreach, and charges the end user for the line and services provided (including calls etc.).

Broadband services can also be provided by alternative operators through WLR.

Who might an ‘alternative telecoms operator’ be? See ‘What about all the other providers?’ below.

What is an ‘alt-net’?

Alt-nets generally build their own networks, laying their own fibre optic cables in the locations they cover. This approach means that they tend to operate in specific, relatively small geographic areas.

The alt-nets, then, tend not to use Openreach and WLR products. As most are relatively new to the market, and because they are investing now, in new networks, they tend to be ‘full-fibre’.

There are many alt-nets across the UK. The largest include CityFibre, Community Fibre, Hyperoptic and KCOM, . In the south west, Gigaclear, Jurassic Fibre, TrueSpeed and Wessex Internet are names you may have come across.

What about all the other providers?

Having distinguished between Openreach, Virgin Media, alt-nets and mobile carriers, a sensible question might be “what about my provider then?”

Some of the biggest Internet Service Providers (ISPs) in the UK generally use WLR and the Openreach infrastructure to provide their services, including:

  • BT (which owns PlusNet and EE)
  • Sky Broadband
  • TalkTalk
  • Vodafone UK
  • Shell Energy
  • Zen Internet

Most ISPs, in fact, will be doing this if they’re not Virgin Media or an alt-net.

PSTN info: what is the PSTN?

The Public Switched Telephone Network, or PSTN, is the term used to mean both the infrastructure and the services that enable public telecommunications.

The PSTN, and the generally available telephone services across the UK, date back in some senses over 100 years. Throughout this time copper cables (generally two, referred to as a ‘copper pair’) have been used to connect telephones in individual premises to ‘Primary Cross Connection Points’ (PCPs), usually referred to as ‘green street cabinets’, and onward to local telephone ‘exchanges’. Linking the exchanges together created the national telephone network, or PSTN.

First as the General Post Office (GPO), and then as British Telecommunications (BT), the PSTN has supplied telephone (or ‘voice’) services over this infrastructure, and latterly added ‘data’ services to it.

Originally using fixed-line analogue systems, about 40 years ago in 1982 the UK government announced that it would sell 51% of ‘British Telecom’ to the public in the first example of privatisation of a public utility. Two years later, in 1984, the first digital international telephone exchange opened in London, and by 1989 BT had spent over £15 billion on modernising services and making the trunk network fully digital.

The PSTN allows calls to be made using ‘analogue signalling’. As broadband services have emerged, and increased in reliability and performance, so the PSTN has changed. The PSTN core network is fully digital, and has been since 1998 (including over 6,000 telephone exchanges), while the ‘edge’ (the bit that connects to local premises) is still often analogue.

A standard analogue telephone line, often presented in a white box on the wall, is referred to as a ‘PSTN line’.

PSTN info: why is the PSTN being withdrawn?

Essentially, because it’s no longer being used in the way that it was, and in the way that would better support and justify maintaining it.

The Ofcom Wholesale Voice Markets Review 2021-26 research found that 96% of households now have a mobile phone. The same research found that businesses made 72% fewer landline calls in 2020 than they did in 2008.

Going back further, up until the 1980s the PSTN infrastructure was almost entirely carrying voice traffic (telephone calls). With the introduction of DSL, the nature of the traffic changed, and the PSTN gradually started to carry more and more data traffic, and less voice traffic.

Three stages of change in the voice and data proportions between the 1980s and 2026

This isn’t what the PSTN was designed for. The priorities for Openreach, looking ahead, are to invest in and grow the UK fibre network, and as a result their legacy infrastructure and equipment making up the PSTN is ageing and becoming more difficult and costly to maintain.

The analogue layers of the PSTN use something called Time Division Multiplexing (TDM): a way of sending multiple signals over a single analogue or digital signal path (i.e., connection). TDM is an obsolete technology, tracing its history back over 150 years and, for example, being employed by the British Army in 1944 (to manage ten telephone calls over a single microwave link across the English Channel).

IP has been gradually replacing TDM for some time, and that process enters a new phase as we prepare for the PSTN switch off (which actually means the TDM switch off).

From the Ofcom Wholesale Voice Markets Review 2021-26 Statement, “in contrast to TDM networks, IP networks are multipurpose networks that provide data services such as broadband internet access as well as telephony. Unlike TDM networks, they do not have dedicated switching functions to connect calls. Instead, calls are encoded as IP packets and conveyed across a common IP network infrastructure that is used for all services.

“IP network architecture differs from that of TDM networks: IP networks typically have a small number of points of connection (POC) located at core network nodes, which are remote from most end-users’ fixed lines. For example, BT’s IP network has around 15 POCs. It also permits interconnection via internet peering or via an internet peering partner.”

What this means is that IP networks are simpler to build and maintain, and more capable than TDM networks like the PSTN.

PSTN info: key dates

The first key date is September 2023: this is the ‘stop sell’ date, which means that Openreach will no longer supply new PSTN or ISDN connections from this time.

And then, of course, there is December 2025, when Openreach intend to withdraw all products reliant on the PSTN, including standard analogue phone lines and ISDN lines.

Of course, it makes a great deal of sense not to wait until these deadlines in order to change to services that will work in the future.

Many connectivity deals, for example, are commercially more attractive over 36 months than 12 months, but a 36 month term starting any time after December 2022 will go beyond the withdrawal date for the PSTN in December 2025.

Key questions: what should I get to replace my PSTN-based connectivity?

Where the PSTN was analogue, its replacements are digital; and where the PSTN was designed to support voice (with data added), its replacements are designed to support data (with voice added).

The rollout of fibre across the country continues, and ‘full-fibre broadband’ is now available to almost 30% of the UK, where ‘full-fibre’ means there’s no copper cabling in the connections between the provider’s core network and the subscriber’s premises.

Where there’s no full-fibre, about 5.5 million premises can use Virgin Media’s ‘fibre + co-axial cable’ DOCSIS network for a high-speed, non-PSTN connection. Together, this means about 47% of homes have access to gigabit-capable broadband.

Where they don’t, Single Order (SO) products from Openreach can be used by providers to deliver broadband services like FttC (SOGEA) and ADSL (SOTAP), but without the ‘dial tone’ and voice services built in.

The specific combination of ‘telco’, technology and product will differ from situation to situation, but in general the replacements will be:

  • an FttP or another ‘full-fibre’ connection;
  • a Virgin Media connection;
  • a SOGEA connection; or
  • a SOTAP connection.

If this all sounds a bit confusing, don’t worry: we’re here to help. Get in touch with us and we can work out what’s best for you.

Key questions: what should I get to replace my PSTN or ISDN voice service?

Once the connectivity is in place then, the voice services need to be added; layered on top, so to speak. VoIP is the main replacement technology here.

In the domestic market (i.e., residential premises), the existing service providers will be offering products that use VoIP rather than traditional voice technology. BT’s Digital Voice product is likely to be used by many, and other providers will offer similar solutions.

For businesses, there will be three main groups:

  1. Those with minimal voice infrastructure at present, which includes many micro-enterprises and businesses that only manage a small number of voice calls;
  2. Businesses that already have IP telephone systems, using the internet to make and receive calls; and
  3. Those with legacy telephone systems, using PSTN or ISDN lines.

Group 1 businesses are likely to find that the same solutions offered to residential settings also work for them. Indeed, many of them will be run from homes.

Group 2 businesses are less affected by the PSTN switch off, and instead only need to consider whether their systems provide the right functionality and value.

Group 3 businesses will need to take action to replace their telephone systems.

When migrating to VoIP from an older phone system, it is possible to retain existing landline numbers or DDIs using a process called ‘number porting’, which is similar to the process when changing from one mobile phone network to another.

VoIP software has also been designed to work on computers, referred to as ‘softphones’, allowing calls to be made and received on a laptop or desktop PC (with a microphone and speakers or headset).

Not all VoIP systems are created equal, of course, and it is important to think through what’s needed in order to maximise the benefits and avoid problems.

We can help with this, so if you’d like to have a chat about it, get in touch with us and we can work through it together.

Key questions: will I pay more for telephony and broadband when the PSTN is switched off?

Currently, domestic subscribers can purchase a PSTN line for making and receiving calls for as little as £10 to £15 per month, while a full Fibre to the Premise (FttP) connection with IP voice is generally at least £40 per month. Although this includes the broadband connection, and is hugely faster and more capable than the PSTN line, it is nonetheless a significant increase for those that just want voice on their lines.

For these customers, low-bandwidth options are expected to emerge but there isn’t enough information about this as yet to provide a clear position or recommendation.

It is possible in the domestic market that the withdrawal of the PSTN will mean paying more, but if prices do increase the better speeds as a result of the ever-expanding fibre network and withdrawal of legacy aspects should also mean value for money increases.

What is known is that the UK has traditionally been quite a competitive market for broadband providers, and that has generally meant lower prices: of the 29 countries in Western Europe, the UK is the fourth cheapest. However, due to lower average speeds the UK has been comparatively poor value for money, ranking 25th out of 29 on a ‘cost per Mbps’ basis.

For businesses, the picture may be slightly different.

Those using ISDN often see much higher charges for calls than can be achieved with newer IP telephony solutions. Many businesses also have good connectivity in place already, and IP-based voice services can be added with what’s called Session Initiation Protocol (SIP), so there are opportunities for many to save money.

There are various different ways to approach it, so if you’d like to know more, get in touch with us and we can go through the options.

Key questions: what benefits are there with a VoIP telephone system?

For businesses, there are many benefits in migrating away from a legacy telephone system to a VoIP system, even without taking into account the issue of the PSTN and ISDN switch off.

Lower call costs

Generally, VoIP calls are cheaper than traditional landline calls. The PSTN is large and quite complex, and costs a relatively large amount to maintain. Calls routed over the networks designed to carry data are simpler, and are growing and improving to meet the increase in demand.

Better scalability

A key advantage is the ability to grow without necessarily needing to buy hardware or install cables. Many users prefer using a VoIP system via their laptop, or an app on their mobile phone, and even physical handsets for desks can connect wirelessly.

Enhanced features

As well as making and receiving voice calls, VoIP systems usually provide a lot more functionality than their analogue predecessors. Setting up conferences, with video and/or audio; messaging services; and ‘presence’ (the availability of a user or device) are often included. Voicemail can be accessed from anywhere, sent to email, or even transcribed.

More flexibility

For many businesses, this is the main benefit: a VoIP system is likely to be a great deal more flexible than a legacy system. Staff working away from the office can do so in the same way they would in the office, with softphones and smartphone apps. Auto-attendants can efficiently manage and route calls, alongside or instead of people. Users can have physical handsets, softphones, headsets, web clients, and smartphone apps, using whichever works best for them.

At Think IT we provide many clients with connectivity and VoIP telephone systems, so if you want to look at how it would work for you, get in touch.

Key questions: what about special line rental services after the PSTN is switched off?

Many businesses that have migrated to VoIP still maintain PSTN lines for various ‘special line rental services’ like alarm systems, payment terminals, fax machines etc.

During the withdrawal of the PSTN, any of these services will need to be replaced, or reconfigured and tested (e.g., with new IP solutions and the ‘SO’ products).