What does the ISDN switch off REALLY mean?

What does the ISDN switch off REALLY mean?

ISDN is the network that is in place to carry your telephone calls and was first launched by BT in 1986 as a means to migrate outdated landline technology to digital. However, in 2015 BT released a statement announcing that it would stop taking new ISDN orders in 2020 with a view to switching off and deactivating its ISDN network completely in 2025.

Given that this will affect so many companies and the fact that scaremongering sales tactics have already begun by some telecom companies, we wanted to put together this article to explain what the switch off will really mean for your business.

The Basics

We know that for most businesses ISDN, PSTN and IP are all just letters, so before we delve any further we thought we would start by covering the basics:

PSTN or Public Switched Telephone Network is the traditional landline setup you are probably most familiar with and may have currently in your business and at home.

ISDN stands for Integrated Services Digital Network and is a digital phone system. While it is a lot newer than PSTN it is nowhere near as advanced as some of the options that are on the market today.

IP stands for Internet Protocol and is the protocol used to carry data traffic across networks. In terms of telecoms, there are two main types: VoIP & SIP. VoIP only carries voice traffic, using IP as the protocol to manage it. Whereas SIP is the underlying technology that will replace your ISDN phone lines.

Why are BT making the switch?

Like all commercial decisions, it is largely driven by cost and profit, in addition to the fact the network has remained largely unchanged since it was first launched, with the introduction of new internet connections making ISDN an outdated legacy system.

Through benefiting from these new faster Internet connections and investing in VoIP, BT can converge all their services to one network and focus their resources into a technology that will allow them to meet the demands of businesses in the future, instead of continuing to spend money supporting an outdated system.

What does this mean for customers?

As of 2020, you will no longer be able to order or purchase traditional ISDN phone lines from BT and you will need to swap your current system to IP. With an estimated 2 million customers still using ISDN it is no surprise that there is uncertainty around what BTs announcement will mean for business communication.

If your current ISDN phone contract is up for renewal soon, then now is the right time to start exploring the option of switching to SIP Lines as a replacement. Make sure and do some research first though, as when using SIP Lines certain building blocks will need to be in place. Our SIP Lines: A beginners guide is a great starting point. 


What are the next steps?

With an estimated 20% of businesses still unaware that the switch off is even happening, you will be glad to know you’re already one step ahead simply by knowing it is happening. That doesn’t mean you should become complacent, the sooner you start considering your options the easier the transition will be for your business as you can spread out the costs of switching. Technology for landline telephony has remained relatively unchanged throughout its time, but now technology has moved on, so you should probably be considering IP telephony regardless of BTs plans. Follow a few simple steps now so your business is in the best position for the switch off.

1. Find out when your contract is due to be renewed

Start by contacting your service provider to find out when your contract is up for renewal. This will give you a better timeline of when your own migration could potentially happen, allowing you to plan in terms of operations and to determine budget and cash flow. Available spend will help when determining which telephony platform is going to suit your business best.

2. Identify if you need a phone system upgrade

A good rule of thumb is, if you have purchased your phone system in the last five to six years, it is possibly SIP capable. Capable however, doesn’t mean ready, the system may need add-ons in terms of hardware or software, which you will need to factor into your migration plans. It is best to determine this as soon as possible to avoid any unforeseen costs. Some of our customers have opted for a hybrid system, which seeks to manage possible costs of deployment by being able to utilise traditional office telephone cabling that older phone systems use but be ready for SIP lines when the switch off comes round.

3. Consider your Internet connection

SIP lines are accessed, not by distinct copper wires coming into your office but over your broadband connection and it has to be up to the job. If you still have ADSL, it’s probably a non-starter. If you have Fibre to the Cabinet broadband services then you at least have the potential to look at SIP lines for an in-house telephone system or to use a Cloud/Hosted Telephony service. It might be worth considering a dedicated line only for voice traffic, to ensure that you never experience any downtime. This is particularly important for businesses where the telephone is business critical.


These simple steps will provide you with at least a better understanding of what the switch off will mean in terms of cost for your business. The good news is you have plenty of time to plan for these costs and additionally with any system upgrade you will also be benefiting from enhanced functionality.


If you have any questions about BTs ISDN switch off, get in touch with a member of our team by emailing [email protected], and we will happily talk you through the options and your own roadmap to migration.

Aaron Maxwell

Field Sales Consultant at BT

5 年

Good article Stuart Lunn?- I agree that the scaremongering is becoming ridiculous.

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