How to be ready for the PSTN switch-off with Teams Voice

How to be ready for the PSTN switch-off with Teams Voice

With ISDN networks reaching end-of-support and PSTN reaching end-of-life in 2025, your organisation needs to be ready for the switch. This blog looks at what you need to do to ensure you move seamlessly into the post-PSTN world, why Microsoft Teams Voice is the best solution, and why it’s important to start planning this now.  

Ofcom have identified that they have every intention to stop the resale of ISDN2/30 circuits to new telecoms providers after September 2023. This also means all existing telephone providers will need to stop providing the service after December 2025. How this will all work, and what their plans for telephony services up to 2026, has all been articulated in a statement from Ofcom.  

The key here is to understand that PSTN will switch off use of ISDN in the very near future. The world of telephony historically has moved at a snail’s pace. Traditional telephone systems would be installed and then left with little assistance other than electricity and a shoestring support contract. However, this meant that there could be no increase in features or functionality from the day of installation.  

The demise of ISDN, therefore, means plenty of opportunity for innovation as part of your organisation’s telephone upgrade.  


What is PSTN? And what is ISDN? 

Integrated Services Digital Network, or ISDN, is how telephone servers have been provided to telephone systems. It was approved way back in 1998 as a method of providing data circuits to subscribers and allowed for voice, video, data, and other network services over a digitised public switched telephone network – or PSTN.  

At its height, more than 25 million subscribers and 1.3 billion analogue lines were in use worldwide. Thankfully this has moved over to digital subscriber lines (DSL) for much of the data use – but telephone systems have lagged.  

There is still a significant amount of ISDN lines still in place – in the UK there are around 160 ISDN channels per 1,000 inhabitants. The UK uses over three times the amount of ISDN circuits as our counterparts in the US. This is likely due to the fact that major US telephone providers began stopping orders as far back as 2013.   

Why are they turning off ISDN and PSTN?

BT recognises that IP telephony is the future of phone communications. With many businesses having already made the move to these new technologies, the demand for legacy systems has decreased dramatically over the last decade. 

What does the PSTN switch-off mean for us as a customer? We still have ISDN!

Good news. Content+Cloud has been working hard at removing older telephone systems and has transitioned tens of thousands of users from older telephony systems to modern Voice over Internet Protocol (VoIP) solutions.  

Ofcom has stated that over two million businesses are still using ISDN connections, so you’re hardly rare in this – but the time is coming at which businesses need to be able to move away from their old on-premises telephone solutions.

Microsoft Teams allows for a hosted Private Branch Exchange (PBX) to be used. There are many sceptics of Teams as a telephone system but more than one billion minutes of telephone calls a month now are made through Teams.  

At Content+Cloud, we have the ability to leverage our expertise to move away methodically from your incumbent telephone systems to ensure there is no loss of service and functionality. With the cloud hosted telephone solution in Microsoft Teams Voice, we’re able to maintain an uptime of 99.99%.  


What do I need to consider?   

Switching is straightforward. Nevertheless, we recommend you consider the following before making a change.   

Your current system   

The number of users you currently have will have some impact on what the best solution for your business will be.   

If you’re a small business using one phone line, then making the switch to a fully hosted solution is worth considering due to low costs, ease of management and scalability, meaning it can grow as your business does. This means you’ll be using Microsoft as your telephone provider for your hosted telephone system as well as providing your telephone lines and minutes – this is known as Microsoft Calling Plan. 

If you’re a larger business with an on-premises PBX, you might want to keep your existing equipment and adapt it to make it suitable for after the switch-off. Should this be applicable, it’s important if you’re considering a SIP solution that your on-premises telephone system supports IP telephony, otherwise it might not be worth the cost of putting a new on-premises system in place to be compatible.  

In most cases, considering Microsoft Teams Voice using direct routing to avoid the high upfront costs is commercially and technically advantageous.  


A reliable and robust internet connection is key to keeping you connected to your customers. Your new system will be reliant on good connectivity speeds, and it is important that you have these in place. We recommend that a network assessment be completed on all new Microsoft Teams Voice deployments – this is part of our standard offering.  

Number porting   

When switching from your incumbent supplier, it is important to plan in your number porting, particularly if you want to use existing numbers or location-specific phone numbers. Depending on the number of numbers to be ported this can take a few weeks so it’s an important point and will avoid any business disruption.  

At Content+Cloud we work with you to do the porting processes for you. We’ll liaise with the existing provider, manage and maintain the porting of all existing numbers, and ensure that your numbers are enabled within Microsoft 365. We ensure that the numbers are ready to allow users, and services such as Interactive Voice Response (IVR), to be enabled and ready for day 1.   


As many businesses have adopted hybrid working or a remote work culture the flexibility of your system should be a consideration. The ability to easily transfer between locations and work seamlessly from home or wherever you choose is a key choice for many businesses.  

Microsoft Teams Voice provides the flexibility and agility needed for staff to contact customers and colleagues as normal from wherever they are working. 


The end of business ISDN lines – the start of something better 

Change of this scale – and particularly in an area so critical to business as telephony – may seem overwhelming. We understand; we’re a business too. However, the need to change is only going to become more urgent.  

Engaging in the process now gives you not just the best chance of moving seamlessly to your new phone system, but also the opportunity to think afresh about how telephony supports your users.  

After a lifetime of rigid telephony systems, we have a chance to innovate and embrace the continuous improvement that the cloud has brought to other workplace tools. That’s not scary. That’s exciting.  

Explore the art of the possible in Microsoft Teams Voice 

PSTN will reach end-of-life in 2025. Is your business ready to see what’s possible with a move to Teams Voice? Content+Cloud is running in-person and virtual workshops to help you understand your readiness for change and build a plan for success with telephony in Teams. 

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