BT PSTN Switch off 2025: Check out our Jargon Busting Guide

Published: 16 March 2022

In business, the way in which we communicate and collaborate is continually evolving. In 2019 BT announced that they will be switching off their old analogue public telephone network and switching over to a fully digital network. We wanted to break down some of the jargon around the digital switchover and explain what this could potentially mean for your business.

Why is BT moving over to a fully digital network?

The technology around us is changing at a rapid pace, especially in our communications, as we now have smartphones, apps, and video conferencing solutions like Zoom at our disposal which rely on reliable fast internet connections.  Our current telephony network relies on a web of copper wires buried beneath our feet. This outdated infrastructure is no longer sufficient for modern communications, as it cannot support the internet speeds we need, so BT has now decided to switch to a fully digital network.

BT has announced that the switchover will be completed in 2025 which is a fully fibre optic / digital network, so every phone line in the UK will be digital, routing calls over IP (Internet Protocol) rather than the traditional PSTN.

Jargon buster:

There is a lot of technical jargon around the BT PSTN switch off, so here are some terms you may find useful to understand.

  •  VoIP: Voice over Internet Protocol
    This is a the transmission of voice and multimedia content via an internet connection.  As an example, when we make a call on a VoIP telephone system our conversation is converted into data packets which are sent across the internet via network switches and routes to the recipient were it is converted back to an audio call.


  • BYOD: Bring Your Own Device
    Since the rise of mobile devices such as smartphones, laptops, and tablets, this terminology has been used to refer to employees who use their own devices for business purposes.  Devices operate within the company’s secure corporate network and may be subject to additional security measures.


  • PTSN: public switched telephone network
    This is the traditional phone network we all know.  It carries only voice calls which are routed to local telephone exchanges to be forwarded to the call recipient.  The majority of PTSN lines use copper wire, BT are wanting to now route calls via fibre and therefore are switching the PTSN lines off by 2025.


  • ISDN: Integrated Services for Digital Network
    A digital version of the telephone line, using traditional copper line networks. This was the first service to allow businesses to send data, such as voice calls or images, through their phone lines using the internet. ISDN will be switched off by 2025 to be replaced with ITSP.


  • ITSP (Internet Telephony Service Provider)
    Internet telephone service providers offer and host digital communications.  They are the modern-day equivalent of telephone exchanges, and use data centres around the world to host servers, switches and routers that are capable of delivering voice and data to any location with an internet connection.


  • SIP (Session Initiation Protocol)
    SIP is used to start, maintain and terminate real-time digital voice, video, and messaging applications over the internet.  The SIP protocol is the basis of VoIP.


  • SIP Trunks 
    A SIP Trunk (a SIP phone line) is the modern-day version of an analogue phone line.  A sip trunk is required for each SIP call made.  They are generally used to connect an on-premise PBX to the customers ITSP.


  • SIP / VoIP Phone
    This phone uses SIP/VoIP to make voice calls over the internet. Unlike traditional analogue phones which were hardwired back to the PBX, SIP/VoIP phones connect to your network switches which send the voice data to the gateway router and out to the internet. The data packets have all the information required to route to the call recipient. Furthermore SIP/VoIP phones do not need to connect to an on-premise PBX as they can connect directly to ‘Cloud Hosted’ PBX systems such as BT Cloud Voice.


  • PBX: Private Branch Exchange
    A PBX is a private telephone network used within businesses.
    It allows employees to communicate internally with each other and with people outside of the company. A PBX allows for free calls between users and sits outside of the telephone network. There are 2 types of PBX –traditional ‘on-premise’ and hosted. A traditional PBX system is located onsite and is restricted to internal company use only. Whereas, a hosted VoIP PBX, uses internet protocol, thereby allowing you to make and receive calls from any location with an internet connection.

BT Cloud Voice

Now that you understand what the digital switchover involves and the jargon around it, it is time to look for a solution to make sure your business is modernised in preparation.

BT Cloud Voice comes with all the functionality of a traditional phone system, except the calls are carried over your internet connection, and unlike traditional phone systems, there’s less hardware to buy! Cloud Voice brings your voice, video, meeting, and messaging tools together under a single, intuitive, and flexible online portal

Watch Our On-Demand BT Cloud Voice Overview Webinar

In preparation for the BT PTSN switchover, Xperience’s John Murray has teamed up with Damien McConville from BT to provide an exclusive on-demand webinar. Grab a coffee and sign-up to watch it below.

BT Cloud Voice Overview | On Demand Webinar

Discover more about BT Cloud Voice: Sign up to our on-demand webinar

About the Author

This article was published by Nicole Cowell, Senior Content Marketing Executive

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