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Switching from ISDN to VoIP: a step-by-step guide

With BT Openreach switching off all PSTN and ISDN services by 2025, many companies are scrambling to find alternatives to replace their traditional phone systems. The telecommunications provider openly endorses digital communications solutions as a replacement for legacy phone systems, which many businesses are looking into.

Voice-over-Internet Protocol or VoIP is one of your best options if you’re planning to switch from ISDN.  VoIP enables traditional phones to operate over computer networks, which means you’ll be taking and making calls using the internet and not traditional phone lines.

VoIP phone systems offer a wealth of business benefits, including an easy setup process. Just follow these steps below to successfully migrate from an ISDN to a VoIP phone network.

1. Audit your current system

The first step is to take a look at your current network and setup. You need to catalogue everything you have now, from hardware and software to processes. Here are some questions you can ask yourself to help with the audit:

  • How many phones do you have? Will you be keeping them or switching to an all-digital system?
  • How many phone numbers or direct-dial-in numbers do you have? How many do you actually need?
  • How do you handle unanswered calls? Do you use voicemails, voice recordings, call routing or call queues?
  • Do you need extensions for different departments and individuals?
  • Do you often use international calling?
  • Do your employees work remotely? What form of communication do they often use when they’re not in the office?
  • Do you need additional services, such as a network security system and network management service?

Answering these questions gives you a more concrete picture of the functions you need to bring and the ones you need to add to your new system. Keep in mind that switching to VoIP doesn’t just involve replacing your business phone system; it’s also a chance to fill in the gaps in your current processes so that your employees will be able to communicate more effectively.

One of the important things to do in this step is to assess your internet connectivity. Most of the common VoIP problems happen due to poor connection, making sure yours is fast and stable enough. You can look into business internet plans that run on gigabit instead of megabit speeds if you need to upgrade your internet connectivity.

2. Draw up a plan

With a clear picture of your current telephone system, you can now draw up a plan for your new system. Identify what you want and expect from your new phone solution, whether it’s to reduce your operating costs, increase your capacity, implement a better business continuity, or a combination of these goals.

When you have your overarching goal, start plotting out the tiny details necessary to achieve that goal. For example, you realise that your business needs a more cohesive remote work communication strategy. List the programs and equipment your employees need to stay productive even when they’re working apart.

Be sure to include your employees’ input about the company’s communication processes since they’re the ones who use these daily. Explore different scenarios that could impact the company’s connectivity – power outages, natural disasters, a pandemic – so you can devise a backup communication solution for each.

Your communication plan is important for the next step since it will determine the VoIP provider you’ll choose.

3. Choose a VoIP provider

The best VoIP service is one that enables multiple communication and management functions for your company. Again, you want to seize this opportunity to upgrade your business’s communication approach, so look for a VoIP provider that offers different add-ons to their service plans.

Choose a service provider that offers excellent support and security. Since your network will be in the cloud, you need strong security measures to keep your network and data protected from cyber attackers. You also want a VoIP provider with accessible support services so you can contact them in case there’s a problem with your system.

Below are some additional VoIP features to consider:

  • Unified Communications
  • Video and Audio Conferencing
  • Advanced Call Routing
  • Mobile App Integration
  • Customer Relationship Management Integration
  • Automated Attendant

4. Think about the hardware

If you still have ISDN phones, you have to decide if you’re keeping them or not. If you are keeping them, you can look into a hosted PBX system. This kind of cloud business phone system has VoIP capabilities, which means it routes calls through the internet.

But if you’d rather let go of your old phones to clear up some space in the office, then switch to a VoIP system. The VoIP technology itself doesn’t require any hardware to run since it resides in the cloud, although you may need additional equipment to ensure your call quality. Consider investing in high-quality headsets that minimise echo and feedback.

If you’re planning to mobilise a remote workforce, ask your VoIP provider how you can connect personal devices to the network and if there are any programs you need to install for your employees.

5. Test your new VoIP lines

Test your VoIP connections once your provider finishes setting up your system. Try calling someone or have someone call you then check the audio quality, latency and connection stability. Does the call suddenly drop? Is there a delay from when you say something to when the other person hears you?

You also want to test the call quality when there’s a lot of network activity. Network congestion may affect the quality and issues like choppy or delayed audio.

Don’t forget to test the other functions of your VoIP system, such as call routing, automated attendant services and remote communication capabilities. If any problem occurs, contact your VoIP provider immediately so they can remedy it.


The success of your VoIP migration is anchored on your planning. Perform an in-depth analysis of your business’s communication strategies so you know exactly how the PSTN switch off will affect you. From there, you’ll need to identify the current capabilities you have and the functions you need to add to improve your business communications.

Ultimately, the goal is to make your company function as seamlessly as possible by giving it the right communications platforms and tools. Be sure to seek advice from a telecommunications expert to know which solution would best suit your unique needs and goals.

Gamma provides cost-efficient solutions to replace PSTN systems, helping businesses cope with the switch off. For enquiries about business communications solutions, fill out our contact form.