Migrating ISDN to SIP | ISDN will be phased out by 2025

Migrating ISDN to SIP

Migrating ISDN to SIP with
Peach couldn’t be easier

ISDN has been a standard for so long that you might have concerns about moving away from a service that already gives you excellent call quality and flexibility. Like all things in the world of Technology, change is coming; companies will inevitably have to migrate ISDN to SIP.

By 2025 you must have completed migrating ISDN to SIP as you will no longer be able to order ISDN; SIP Trunks will be in its place. We understand that many businesses may be hesitant about migrating ISDN to SIP, read on and take action sooner rather than later.

What are the benefits of SIP over ISDN?




  • Requires dedicated installation costs

  • Rental costs on average £15 - £20 per channel

  • Call costs on average can be up to 25% more expensive

  • Can use existing planned or dedicated connectivity at a much cheaper cost

  • Rental costs usually £5 - £10 per channel

  • Free calls between sites connected on network locally and internationally


  • ISDN2 has 2,4,6,8 channels
    ISDN30 has 8 to 30 channels

  • ISDN30 requires sequential DDI ranges with a maximum of 5 different ranges

  • Can only increase/decrease channels with Open reach planning. Once an ISDN30 has 30 channels, a new bearer is required for additional channels.

  • SIP can have 1-2,000 channels on one connection

  • No limitations on DDI ranges

  • SIP can expand/decrease instantly


  • Can only use local geographic pre-fix numbers from the local exchange

  • Needs to be diverted by network provided and can only divert main bearer numbers

  • Lead time for ISDN installs can be 2-8 weeks

  • Use any geographic and international number

  • Can be diverted instantly and can divert by DDI

  • Can be delivered instantly, depending on current connectivity

Myth Busting

  • Migrating ISDN to SIP

    Business Continuity

    Keep your business running with minimal disruption. You can be prepared for any situation, put in place a disaster recovery plan and have us set up backup facilities. You can re-route calls instantly in emergency situations.

  • Migrating ISDN to SIP


    If your business has multiple sites, SIP trunking can rationalise the number of PBX’s you’ll need to maintain and the maintenance costs with no loss of control of your telephone numbers. This means you get to keep your phone numbers.

Myth Busting

  • Migrating ISDN to SIP

    Is it secure?

    When SIP trunks are implemented correctly, fraud is not an issue. Connectivity will be more secure than previously. A properly configured SIP channel will allow you to handle your connectivity via dedicated firewalls or a router with firewalls built in, which is managed by Peach Technologies.

  • Migrating ISDN to SIP

    It’s new and untrustworthy!

    SIP has been around since the mid-1990’s, and SIP trunks have had a presence since 2007, the technology has been in use for some time. It is safe to say there is a substantial body of expertise in the marketplace today, and that the technology is well tested and up to date.

  • Migrating ISDN to SIP

    Call quality won’t be as good!

    SIP Trunking uses private IP connections specifically designed to carry voice, and as such come with Quality-of-Service guarantees. Therefore, can deliver the same or even better call quality than ISDN. We provide an expert SIP service, dedicated support and SLAs.

  • Hosted Telephone Systems

    Migrating will be a hassle

    Deploying SIP Trunks is a more straightforward process than with ISDN, Peach puts a good plan in place before you start your project. Full onsite support is provided so you won’t be left to cope with any issues yourself.

  • Hosted Telephone Systems

    It will cost too much!

    Upgrading to SIP will have the opposite effect, it will save you a significant amount of money. You’ll save most noticeably when no longer paying ISDN line rental costs. Additionally, you’ll have access to lower call rates or in some cases, free calls to UK destinations or mobiles.

  • Migrating ISDN to SIP

    SIP will complicate everything!

    The reason businesses like SIP so much is that it helps when it comes to rationalising and streamlining telephony. This is particularly useful for companies operating on a multi-site basis, and as BT are phasing out ISDN anyway there really is no choice in the matter.

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