The trend to stop offering ISDN as an option started with US telecoms giant Verizon ceasing to offer ISDN services to new customers. Similarly, in Europe the upward trend was continued when in 2015 BT announced their plan to migrate all users to IP networks and completely switch off ISDN and PSTN services by 2025.

Although BT did not specify the reasons behind cutting off ISDN, the announcement didn’t come as a surprise since ISDN had been facing a decline year on year. According to Ofcom’s Communications Market 2016 Report, there were 7.6 million business fixed lines and ISDN channels at the end of 2015, 2.0 million (21% fall) fewer than there had been at the end of 2010.

PSTN ISDN SME fixed broadband lines Ready for the ISDN switch-off


The decline of ISDN


Even though ISDN has been diminishing for a while, there are still 3 million ISDN channels in the UK, as we can see on the graph above. It might be true that BT does not have all of these channels on their network, yet a considerable number of customers are BT’s and they will be left with no choice but to migrate in the near future. That is why it’s important to future-proof your business and get familiar with SIP lines and VoIP to ensure you don’t get stuck with legacy technology.


At Wavenet we only work with the leading SIP providers in the UK - which we recommend to help you make the transition seamless.

Offering reliable voice connectivity between your PBX and their network. The benefits include increased flexibility, control, resiliency and reduced costs. 



Here are the top 4 benefits of SIP over ISDN:



phone traditionalNumber portability and flexibility

There is not geographical location requirements for numbers and SIP permits out-of-area numbers to be used since your phone number is attached to an IP address instead of a physical telephone line. So, for instance a New York number may point to an office in London. Additionally, ISDN takes 6-8 weeks to implement, whereas SIP takes 24 hours to spin up and spin down.




The bottom line is important for every business and with SIP savings are substantial. With ISDN your voice and data are on different lines, whereas with SIP you can reduce costs by having them on the same one. Also, SIP trunks can greatly reduce call charges including international calls and free calls between multiple sites and offices on the same network.

You can calculate the cost savings of adopting SIP with Gamma’s SIP vs. ISDN cost calculator and see for yourself.



Analytics Icon UCScalability

SIP is deployed across your business’s existing WAN which means that you can add additional trunks in high demand and subtract them in low demand respectively in order to easily scale your telephony needs according to your business needs.



WinnerDisaster Recovery

Incidents happen and at some point your service could be interrupted by a network failure, a hardware problem, natural disaster or just bad weather. Luckily,  one of the biggest benefits of SIP Trunks is the better reliability and much simpler disaster recovery when compared to legacy phone systems. If your business needs a zero downtime environment, SIP trunks allow automatic failover solutions to be implemented so that your numbers will divert to other locations without loss in service.

We hope this article has been of interest. If you want to migrate to SIP please contact us and we will be happy to help.

Our solutions have been evolved over the last two decades to allow us to innovate and provide our customers with the future-proof technology they need to stay ahead of their competition. Broken into seven simple groups, our solutions cover all aspects of business communications, technology and cybersecurity.
  • Networking & Connectivity
  • Unified Communications & Voice
  • CyberGuard
  • TeamsLink & Collaboration
  • IT, Cloud & Technology
  • Contact Centre
  • Mobile Solutions & IoT


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