If you’re currently relying on ISDN, you’ll probably have heard BT announcing the end-of-life (EOL) of ISDN services, with a switch off date of 2025. This will leave many businesses looking for modern alternatives to future-proof their communications for the foreseeable future. The ISDN standards were created in the late 1980s when the world wide web was just being invented, faxes were commonplace and mobile telephony was in its infancy.


Find out how much you could save

It takes seconds to use our ISDN vs SIP calculator to find out how much you could save by switching from ISDN to SIP trunking.

ISDN vs SIP COST Calculator

ISDN was cutting-edge technology when it launched, but much has changed since in the world of business. Remote working and hot-desking are now the norm, along with businesses making use of both mobile and fixed line telephony services.

In comparison to modern counterparts, ISDN is not as efficient or resilient, with disaster recovery being slow. Setup is also slow and can often be expensive, restricting your business's agility.

Why are businesses now looking at SIP trunking as a replacement, and what are the benefits?

Even before the announcement that ISDN had been given an end-of-life date, many businesses were already looking at replacement solutions in order to drive efficiencies, cost savings and help foster modern collaborative working practices which aren’t achievable with ISDN, which has been steadily declining in popularity.

  • Cost reductions with significant savings to be made on line rental and call costs. SIP trunking services will also reduce your costs associated with ISDN PRI trunks, PSTN gateways and service provider contracts.
  • Improved resilience with built-in disaster recovery provisions. SIP trunking provides a solution that can cope with a network outage, emergencies, or lack of connection. It can be easily and efficiently rerouted to back-up sites, with minimal disruption to your voice communications.
  • Increased visibility of performance metrics, to improve productivity and overall business performance. SIP trunking also makes it simpler to manage your billing and reporting, giving you greater visibility into what is being spent.
  • Increased flexibility and scalability to meet the changing needs of your business. Balance calls during peak periods for an overall better experience. SIP offers you more control of your calls by allowing you to add more lines when your demand is high, reduce them when there is little demand or split your calls instantly for efficient handling.
  • Enhanced quality of service for customers. SIP trunking delivers superior call quality compared to ISDN. By using private IP connections specially designed to carry voice, it’s also backed by quality-of-service guarantees.

SIP vs ISDN cost calculator

Discover for yourself the potential savings you can make when migrating from legacy ISDN to SIP trunks. Simply input your current ISDN capacity and we’ll calculate the potential costs if you move to SIP trunking. If you like what you see, get in touch with us and we’ll be happy to provide more detail on your savings and the first steps to migration.

Your Current ISDN Setup

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The Savings calculated in this model are indicative only and do not constitute any contractual obligation on behalf of Nexus Open Systems. Read our full terms and conditions.