HomePSTN Switch Off

Colt continues to support ISDN services

Everything you need to know ahead of the PSTN switch-off.


Act now to futureproof your services

All operators, including Colt, are modernising their voice infrastructure and are moving to IP. In contrast with most other providers, Colt has no plans to end ISDN services at present and will continue to support the market by offering an ISDN over IP solution.

For customers that still require ISDN using a TDM PBX, Colt offers “Voice Line (v)”, an ISDN over IP service, which provides a seamless upgrade path to SIP Trunking on a future-proof platform.

Colt aims to help as many customers as possible to migrate swiftly to futureproof solutions – a change which is largely transparent and requires little to no physical adaptation at customer sites, apart from the installation of the Colt Voice Gateway next to the PBX. Customers can retain their access to the ‘PSTN’ with their traditional PBX while Colt ensures the network is future proof across all operators. The service is offered in the following European countries: Austria, Belgium, Switzerland, Germany, Denmark, Spain, France, Ireland, Italy, The Netherlands, Portugal, Sweden and the UK.

For existing Colt Online users, the Service Guide is available here.


Request a quote for Voice Line (v)

Your choice of communications service is as unique to your business as your voice requirements. 

We'll ask you for a few pieces of information to request a quote in less than 2 minutes.


What service is right for you?

Of course, Colt also offers pure VoIP with Cloud Voice and SIP Trunking solutions. If you cannot make up your mind about which solution is most beneficial for your now, see below:

ISDN Decision Tree

More information about all future proof voice services offered by Colt can be found here.


Other services

In order to maintain the highest levels of availability and service for our customers, Colt is continuously optimising its network. Colt has recently removed SDH technology and migrated customers to newer and highly reliable Ethernet, IP and VoIP technology alternatives. 


Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network (PSTN). ISDN is mainly used for telephony.

It’s happening right now ! In most countries in Europe, the traditional public ‘switched’ telephony network (PSTN) is going end of life. The public telephony network will remain, only the old ‘switched’ technology is being replaced with all IP networks.

In the UK for example, BT Openreach has announced it intends to switch off the traditional, copper-based telephone network in 2025. This is commonly referred to as the PSTN Switch Off.  While 2025 may seem a while away, from September 2023 you won’t be able to purchase any ISDN or PSTN-based services, with many locations affected by a stop sell much sooner than than that.

VoIP is the main successor in terms of technology for ISDN. VoIP, or Voice over Internet Protocol, means that telephone services can be delivered over the internet. This brings a huge degree of modernisation, resulting in greater quality, consistency and extra functionality. 

For pure VoIP services, users require IP Phones or headsets. An IP PBX (telephone system hardware) is set up on premise or in a datacenter, or can be entirely replaced by Cloud Voice services with a virtual PBX also supporting Unified Communications and Collaboration tools (UC&C).

Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for voice calls, the delivery of voice communication sessions over Internet Protocol (IP) networks, such as the Internet.

The broader terms Internet telephony, broadband telephony, and broadband phone service specifically refer to the provisioning of voice and other communications services (fax, SMS, voice messaging) over the Internet, rather than via the public switched telephone network (PSTN), also known as plain old telephone service (POTS).

An easy way to check if your business relies on PSTN is to look for a box on the wall where lines might be coming in. Any lines or connections that don’t come in via your router or internet connection could be a sign you’re connected via the PSTN.

ISDN services use on premise telephone systems (TDM PBX) and each user calls with a digital phone.

If you’re still not sure if, how or where you might be using the PSTN, contact your communications provider or the manufacturer of the equipment and ask them if they work on a digital phone line.

Just be aware that, even if you think you’re connected via fibre broadband, you may be running on an FTTC service. This means you are still relying on old copper wiring to deliver connectivity to your services.

All businesses will need good broadband connectivity to support even the most basic telephony functions.

In the age of digital voice communications, however, it’s worth considering how connectivity could be the defining factor of success; the better your connectivity, the better your business will be able to capitalise on the huge range of digital solutions aimed at delivering flexibility, speed, resilience and cost-effectiveness, as well as superior call quality.


United Kingdom

Nov 2017

Switch-off announced

BT Openreach announces its intention to switch off the PSTN in 2025.

Dec 2020

Stop-sell trial begins

Stop sell begins at Salisbury trial site.

Oct 2021

Stop-sell expanded

Stop sell announced at 169 Exchanges across the UK.

Dec 2022

Switch-off begins

PSTN is completely switched off at the trial site.

Sep 2023

UK-wide Stop-sell

All PSTN and ISDN services will be closed to new customers, and there will be no upgrades or new features available for existing customers.

Dec 2025

PSTN & ISDN switched off

PSTN and ISDN services will be switched off across the whole of the UK.


Nov 2018

Stop-sell of analogue lines

Continued support of existing lines

Nov 2019

Stop-sell of ISDN services (RNIS)

Continued support of existing T0 (BRI) and T1 (PRI) lines.


Technical end of life of PSTN network (RTC)

Gradual migrations to VoIP, phased per geo zones.

Request a quote for Voice Line (v)

Your choice of communications service is as unique to your business as your voice requirements. 

We'll ask you for a few pieces of information to request a quote in less than 2 minutes.