22 August 2022

It is common knowledge that ISDN is a dying technology. BT will switch their ISDN network off entirely in 2025 and the general consensus is the technology will be as good as gone within five years. But this traditional system is still being used by many businesses.

Higher line rental costs for ISDN-based PBX systems are pushing IT managers to consider broadband and ethernet-based VoIP solutions which are better value for money. In this article, we will be looking at what is best for your business.

ISDN vs SIP trunks

Major telecom operations still provide ISDN links. However, for most businesses, this legacy technology is too expensive, too limited, and too inflexible. 

SIP trunking is a next generation technology that works over data connections, such as broadband ethernet. On the other hand, ISDN requires a special line that can cost your business a lot if you decide to move premises. SIP trunking allows for almost unlimited capacity without the huge setup costs.

Hosted or On-site?

SIP trunking is cheaper and more flexible than ISDN, making it the sensible choice for your business. The biggest decision is whether to choose to maintain an IP-PBX on-site or opt for a cloud-hosted solution.


Managing an on-site IP-PBX is almost the same as managing an ISDN equivalent. In this scenario, your IT or telecoms team may need to:

  • Create and manage new extensions and call groups.
  • Source and install additional hardware as your team grows.
  • Configure and deploy handsets to end users.
  • Commission new broadband connections to handle increasing call volumes and VoIP traffic.

Most of the above can be outsourced to an expert service provider, however, there are some drawbacks to an onsite PBX, including:

  • Day-to-day management costs associated with keeping the PBX running.
  • Additional hardware and licensing costs.
  • Configuration issues when creating intersite links.
  • Harder to create a service that supports routing of calls.
  • Localised disasters could take your entire phone system out of action if the PBX is affected.

Cloud-Based Hosted Telephony

Many businesses are now turning towards hosted cloud services. From the smallest SME to large enterprises, cloud solutions are increasing in popularity. There are a few reasons why, such as:

  • Onsite PBX isn’t needed, all call routing is performed by the system via the internet.
  • In-house support costs are reduced.
  • Additional capacity, such as new extensions can be added via a web interface.
  • Set-up is little more than plugging a VoIP handset into the network or downloading an app onto your device of choice.
  • You can tie mobile phones into the existing telecoms infrastructure. Employees can answer calls wherever they are.
  • Calls between VoIP extensions are free regardless of where the caller is located.


There are a few things to think about when choosing the option that is best for you. Make sure to consider cost, flexibility, location, and ease of management.

Square One Network can help you give advice on which solution is best for your business.

Get in touch with one of our experts today to learn more.