If someone at your charity has mentioned “telephony”, maybe a supplier, a board member, or something you read about the 2027 landline switch-off, and you’re not completely sure what it means, you’re not alone. It’s one of those words that gets used frequently but rarely explained.
The great news is that the idea behind it is much simpler than the terminology can make it sound.
This guide breaks down what telephony means, the main types of systems you’ll come across, and the handful of terms worth knowing, in plain English. No telecoms background necessary.
What Is Telephony? (Definition & Meaning)
Telephony is the technology and systems that permit people to communicate by voice over a distance. Today, that can also extend to video and other forms of real-time communication.
In practical terms, telephony covers much more than the traditional telephone sitting on a desk. A call could travel over an old-fashioned telephone line, a mobile network or an internet connection and still fall under the broad umbrella of telephony.
So, is telephony the same as a telephone? No.
A telephone is a device. Telephony is the wider technology, network and systems that make communication possible. Think of the telephone as one of the tools you use to access a telephony system.
That distinction matters because modern charities are no longer constrained to physical desk phones. Staff might make and receive calls through laptops, mobiles, headsets or Microsoft Teams while keeping the same organisational telephone number.
Even familiar consumer apps illustrate how broad the definition has become. When you make a WhatsApp voice call over the internet, for example, you are technically using a form of internet telephony, even though most of us would simply say we were making a call.
For a charity, telephony could mean a single landline at a small community centre, a dedicated donation hotline taking calls from supporters, a service user helpline offering advice and support, or a cloud phone system connecting staff and volunteers across a larger regional charity’s offices.
A Brief History: How Telephony Has Evolved
For many years, telephone calls in the UK were primarily carried over the Public Switched Telephone Network (PSTN). This is the traditional telephone network most people associate with copper lines and conventional landline services.
Business communications then became more sophisticated with technologies such as ISDN (Integrated Services Digital Network). ISDN provided digital telephone services and allowed organisations to handle multiple calls and services more efficiently than older analogue arrangements.
The next key shift has been towards VoIP (Voice over Internet Protocol). Instead of depending on a traditional telephone line to carry a voice call, VoIP turns voice into digital data that can be carried using IP-based networks. Cloud telephony extends that idea further by hosting much of the phone system away from the charity’s premises and making it accessible through an internet connection.
This is why terms such as PSTN, ISDN and VoIP can sometimes seem to overlap: they belong to different stages in the evolution of business communications.
The direction of travel is now firmly towards digital, cloud-based and progressively more integrated communication. In Qlic’s Future of Telephony webinar, Neel Mavji walks through what that changing landscape means for charities, including where modern phone systems are heading, and what to keep an eye on as traditional systems disappear.
Why Telephony Matters for Charities Right Now
Telephony has become a remarkably important subject because the UK’s traditional phone network is being retired. Ofcom has confirmed that Openreach is retiring the PSTN network nationally by January 2027, with all providers that rely on its infrastructure following the same timetable.. That means charities still depending on legacy services need to understand what their current setup depends on and what will replace it. For more detail, read about preparing for the landline switch-off or our guide to cloud-based telephony for charities. If retaining an existing telephone number is a concern, you can also find out how to port your number to VoIP without losing it.
What Is a Telephony Service? And What Is a Telephony Network?
The terms telephony service and telephony network are sometimes used as though they mean the same thing, but there is a valuable distinction.
A telephony service is what your charity uses. It is the service supplied by a provider that enables you to make, receive and manage calls. Depending on the setup, this could include telephone numbers, voicemail, call routing, auto attendants, support and administration.
The aim is usually that your charity does not have to manage all the underlying technical infrastructure itself. Staff basically need a reliable way to communicate.
A telephony network, meanwhile, is the infrastructure that carries communication between one point and another. Depending on the technology involved, that infrastructure may include physical telephone lines and exchanges, mobile infrastructure or IP-based network connections.
One straightforward way to picture the difference is to think about travelling somewhere by taxi. The network is the road system that makes the journey possible; the telephony service is the taxi company that provides and manages the service you use on those roads.
For most charity leaders and operational teams, identifying that basic distinction is enough. You do not need to know precisely how every part of the network works to make an informed decision about the service your organisation requires.
The Main Types of Telephony Systems (and How They Differ)
Most telephony terminology becomes much simpler once you understand that some terms describe the network carrying the call, while others describe the system that manages calls inside an organisation.
Here are the main types charities are expected to encounter.
PSTN
PSTN stands for Public Switched Telephone Network. It is the traditional telephone network that has conveyed landline calls for decades.
For many people, this is what comes to mind when they think of a regular landline: a fixed telephone service historically associated with the UK’s copper telephone infrastructure.
The significant point for charities is that PSTN is legacy technology that is being retired. Ofcom explains that the network is old and becoming harder and more expensive to maintain, while providers are advancing landline calling towards digital technology such as VoIP.
If your charity still has traditional telephone lines, it is consequently worth establishing whether any of your services still depend on the PSTNrather than assuming that a familiar-looking desk phone tells you what technology is running underneath it.
ISDN
ISDN stands for Integrated Services Digital Network. It provided digital communication over traditional telephone infrastructure and became widely used by organisations that needed more capability than a basic analogue telephone line.
For businesses and charities, ISDN could support multiple simultaneous calls and was commonly used alongside office phone systems.
Although ISDN was an important step forward from analogue telephony, it now belongs to the older generation of fixed telephone technology. Charities encountering ISDN in contracts, invoices or conversations with suppliers should generally regard it as a legacy system that needs to be planned for as part of the move towards modern digital telephony.
PBX/PABX
PBX stands for Private Branch Exchange. A PBX is in effect an organisation’s private telephone exchange or switchboard.
Its job is to manage and route calls. For example, when somebody calls your charity’s main telephone number and selects an option for fundraising, finance or support, a PBX can help route that call to the precise person or group.
Traditionally, PBX systems often meant physical equipment installed at an organisation’s premises. Modern cloud telephony can provide many of the same call-management functions without forcing the charity to maintain a large on-site telephone system.
You may also encounter PABX, meaning Private Automatic Branch Exchange. Historically, “automatic” distinguished systems that routed calls automatically from older manual switchboards. In modern conversations, PBX and PABX are often used to describe essentially the same type of organisational phone exchange, and PBX is now the more frequently used term.
VoIP
VoIP stands for Voice over Internet Protocol. In simple terms, it allows voice calls to be carried using IP-based networks instead of a traditional PSTN telephone service.
For charities, this can make the phone system much more flexible. Staff may be able to use a desk phone, computer or mobile application rather than being tied to a particular telephone socket or office desk.
Modern VoIP services can also provide functions such as call queues, voicemail, auto attendants, call forwarding and reporting. Hosted or cloud-based VoIP moves much of the underlying system away from equipment kept in the charity’s office, with the service provider managing the platform instead.
Because internet connectivity plays a principal role in cloud communications, charities considering these systems should also look at the reliability of their connection. For some organisations, business-grade broadband will provide the connectivity they need, while charities with heavier usage or more demanding requirements may consider dedicated leased lines.
VoLTE
VoLTE stands for Voice over LTE. LTE refers to the technology behind 4G mobile networks, so VoLTE essentially means making voice calls using a 4G mobile network.
Although VoLTE and VoIP both involve voice being carried digitally, they should not be treated as duplicate terms. VoIP generally describes voice communication using Internet Protocol, commonly associated with internet or cloud-based phone services. VoLTE is specifically a mobile-network technology used to deliver calls over 4G.
For a charity, this distinction is beneficial when thinking about staff who work away from the office. Outreach teams, fundraisers, service delivery staff and other mobile workers may depend heavily on mobile connectivity as part of the organisation’s wider communications setup.
That means telephony planning does not automatically stop at the office phone system. Appropriate charity mobile packages can also form part of keeping dispersed teams connected.
Teams Voice/unified communications
Modern telephony is gradually being integrated with the applications charities currently use rather than operating as a separate system.
Microsoft Teams Voice is a good example. Instead of using Teams only for internal chat and video meetings, organisations can integrate external telephone calling so staff can make and receive phone calls through Teams.
For charities already working heavily within Microsoft 365, this can bring different forms of communication into one familiar environment. Staff can work from the office, home or another location while accessing their organisational calling tools through Teams.
This approach is part of a broader idea known as unified communications: bringing services such as voice, video, messaging and collaboration together rather than making staff jump between separate systems.
Teams Voice for charities can turn Teams into a more complete phone system, including features such as external calling, call routing and voicemail.
An Example of Telephony in Everyday Charity Use
The terminology makes more sense when you see what telephony looks like in a real charity.
Age Concern Orpington supports older people in the Orpington area through services including social engagement, wellbeing support and practical assistance. Dependable communication matters because callers may include older or vulnerable people seeking support.
The charity’s previous telephony setup lacked flexibility and made calls particularly difficult to manage outside normal working hours. That created a genuine operational risk: vital enquiries could be missed when staff were unavailable.
The answer was not purely to add more phones. Age Concern Orpington moved to a cloud-based telephony platform, with an automated attendant configured to manage out-of-office calls. This meant callers could be properly directed or informed even when staff were unavailable. The system also provided centralised management without adding unnecessary technical complexity for the charity’s team.
It is a practical illustration of what telephony means in practice. The technology itself is only part of the story. The real purpose of the system is to answer an everyday communication problem: helping the right calls reach the right place and reducing the likelihood that somebody who needs the charity is missed.
Telephony Trends and Terms Charities Should Know
The overall direction of charity telephony is away from legacy, premises-based phone systems and towards digital, cloud-based and integrated communications.
The 2027 PSTN retirement is accelerating that shift, but it is not the only reason for it. Charities progressively have staff and volunteers working across offices, homes and community locations. A phone system devised around a fixed desk in a single building does not always fit that reality.
Cloud-based systems can allow users to access organisational calling from different locations and devices, while platforms such as Microsoft Teams gradually combine telephony with the collaboration tools staff already use.
Our research, Qlic’s 2026 charity telephony survey found that just 14% of charities still rely on a traditional PBX system, while 40% use hosted VoIP and 26% have adopted Microsoft Teams Phone.
For anyone who needs a quick reference rather than another technical explanation, these are the core terms worth memorising:
Telephony Term | Plain-English Definition |
|---|---|
VoIP (Voice over Internet Protocol) | Technology that carries voice calls using IP-based networks rather than a traditional PSTN telephone service. |
PBX (Private Branch Exchange) | A private phone system or exchange that manages and routes calls within an organisation. |
PABX (Private Automatic Branch Exchange) | An automatically operated private telephone exchange; today, the term is commonly treated as broadly equivalent to PBX. |
PSTN (Public Switched Telephone Network) | The UK’s traditional landline telephone network, which is being retired. |
VoLTE (Voice over LTE) | Technology used to carry voice calls over a 4G mobile network. |
Unified Communications | An approach that brings voice, video, messaging and collaboration tools together in one connected environment. |
You do not need to remember every acronym. What matters is being able to recognise what each one largely describes.
If a supplier tells you that your charity has a “legacy PBX connected to PSTN or ISDN services” and recommends moving to “hosted VoIP” or “Teams Voice”, that sentence can sound technical at first. Once the terms are translated, however, it simply means that an outdated phone system and network are being replaced by a modern digital alternative.
That is the level of understanding most charity decision-makers need. You do not have to become a telecoms engineer; you need enough knowledge to ask reasonable questions, understand the answers and make sure any proposed system fits the way your charity works.
Conclusion
Telephony can sound like a specialist subject because it comes with decades of terminology, but the underlying idea is straightforward: it is the technology and systems that allow people to communicate over distance.
PSTN and ISDN belong to the older generation of telephone infrastructure. PBX and PABX describe systems that manage and route an organisation’s calls. VoIP carries voice using IP-based networks, while VoLTE handles voice over 4G mobile networks. Cloud telephony and unified communications take those capabilities further by making calling more flexible and integrating it with the tools people use every day.
For charities, recognising those basics is becoming increasingly important as traditional telephone infrastructure is retired and digital services become the norm.
The important thing is that you now have enough context to have an informed conversation about your charity’s own phone system. You can ask what technology you currently use, whether any legacy services remain, what a provider is proposing and, fundamentally, why a particular solution is appropriate for your organisation.
If you want to talk through what any of this means for your charity specifically, Qlic’s telephony team is happy to have that conversation in plain English, no jargon, no pressure.
