Can I switch from ISDN to VoIP?

With the 2025 UK PSTN (Public-Switched-Telephone-Network) switch off on the horizon we have been approached by a lot of companies this year asking the very same question. Can I move my business phone number(s) from ISDN lines to VoIP?

The simple answer to this question is YES, it is possible to port an ISDN phone number to VoIP. At SiPalto we have been helping companies switch from ISDN onsite phone systems to our SiP Cloud business phone system for over 10 years.

The process is called Number Porting , which allows you to transfer your existing phone number from one service provider to another. The process of porting an ISDN phone number to VoIP involves a few steps:

  1. Choose a reliable VoIP service provider that supports number porting and offers the features and services that meet your business needs.
  2. Confirm with your chosen VoIP provider if they can port your ISDN numbers. Some providers may have specific requirements or limitations regarding number porting, so it’s essential to check their policies beforehand. If porting your numbers to SiPalto it is unlikely you should have any problems but we will always perform the nesessary checks before hand to ensure it is possible.
  3. Verify porting authorisation. This typically involves submitting a Letter of Authorisation (LOA) also known as a Porting Request Form to your current ISDN service provider. The LOA grants permission for the new provider to contact the old provider on your behalf and process the transfer of the phone numbers.
  4. Coordinate with both providers: During the porting process, coordination between your ISDN service provider and your VoIP provider is crucial. Both providers need to work together to ensure a smooth transition and minimise any downtime. At SiPalto we take care of the entire process on your behalf and keep you updates along the way.
  5. Timeframe and downtime: The time required to complete the porting process may vary. It typically takes 5-15 working days, it’s important to note that there may be a brief period of downtime during the switch from ISDN to VoIP. Your VoIP provider should provide you with an estimated timeframe for the porting process. At SiPalto this is typically instant or no more than a few minutes and the porting day will be pre-chosen mutually to ensure we are prepared well in advance of that date.
  6. Test and verify: Once the porting process is completed, test your new VoIP service to ensure that your ISDN number is properly routed to your VoIP system. Verify that all incoming and outgoing calls are functioning as expected. We test all numbers thoroughly upon port completion to ensure there are no issues.

We are always happy to speak to companies who are unsure or nervous about this process, or feel they have not been given all the information from their current provider. Get in touch if you have any questions or need more information about number porting or any other VoIP related questions. We are experts in number portng.