SIP Trunk ISDN Switch Off

SIP Trunking

Are you ready
for the ISDN
switch off?

PBX System

SIP Trunks

A cost-effective
alternative to ISDN
that provides
flexibility and


In 2025 BT will switch off the traditional ISDN network and such services will be replaced by more modern and cost-effective solution.

Businesses will now need to start making decisions as to what to do to ensure business continuity. SIP trunking is rapidly replacing ISDN services. SIP trunks offer a more flexible and lower cost alternative to ISDN for inbound and outbound voice calls.

SIP trunks connect your site directly into a SIP providers network via an IP connection to carry and terminate your inbound and outbound voice calls across the public telephone network.

What is SIP Trunking?

SIP trunking is a standards-based replacement for traditional ISDN. It connects your PBX to the PSTN via broadband, ethernet or private circuit into our national network.

Compared to ISDN our SIP trunking service is less costly per channel and more flexible in how and where geographic telephone numbers can be used. It's also quicker to install and provision and, as standard, it delivers extremely robust business continuity.

The service can support connections ranging from two channels for small PBX-equipped businesses to an unlimited number of channels for large enterprises and contact centres.

SIP Trunks

With our SIP Trunks, you get a service that is more robust and cost-effective than ISDN. Because SIP trunking is an IP-based telephony service, you also get number flexibility, which gives you a whole host of other added benefits that can solve real business issues.

Any business with a PBX can switch to our SIP trunking service and immediately benefit from a more flexible, less expensive and more resilient phone service.

Whatever your current situation is, SIP trunking has an ideal solution to offer your business moving forward.

What is your scenario?

If you are looking to upgrade your current system, it is important to know your options. Take a look at the scenarios below, to evaluate your current business infrastructure and get an idea of which solution is best for your company, Each scenario will explain how your business can make the move to SIP.

Traditional PBX with ISDN2/30

With a traditional PBX phone system, you will already have a physical box on site, this will typically be located in your office's telecoms cabinet and connects to an ISDN2 / ISDN30.

This set-up has been around for a long time, but as 2025 approaches they will no longer be compliant for connection to ISDN2 / ISDN30.

You can however upgrade your business phone service without changing your PBX, which will significantly reduce your costs.

Learn More Get Started

IP PBX with ISDN2/30

If you are using an IP PBX with ISDN, you have already upgraded your system.

Your organization has made an investment in an IP PBX system and if it's affordable and working for your company, you may want to stick with it.

Your equipment and software are ready, however your ISDN lines will need to be converted to SIP Trunks.

Learn More Get Started

IP PBX with SIP Trunks

If you have an IP PBX with SIP Trunks in place, then you are already using the correct technology and do not have to make any changes to your equipment.

However you may want to consider evaluating your SIP Trunk costs.

Irrespective of your industry we have a solution. From small to large organizations including; Hotels, Schools, Care Homes and Call Centres.

Significantly reduce your SIP Trunk costs with SIP

Learn More Get Started

Move to a Cloud Solution

Hosted Telephony

If you are still relying on a traditional PBX in your organisation, it could be time to consider moving to a hosted solution to realise all the benefits that cloud-based telephony has to offer.

Hosted telephony is a telephone system that resides in the cloud rather than in your office. Users access the system through a standard IP handset or a softphone - a screen-based virtual phone with headset. Calls are made and received over a broadband connection.

Learn More Get Started

Our SIP trunks work seamlessly with each of
the leading IP PBX brands in the UK market

Vendors we work with

Vendors we work with

The Benefits of SIP Trunking

Save Money

SIP Trunking enables businesses to save up to 50% on line rentals and 25% or more on call costs.

Number Flexibility

SIP trunking enables you to move office and keep the same geographic number without any ongoing costs.

Business Continuity

If your office has to be temporarily relocated in an emergency, this can be achieved quickly and cost-effectively with SIP trunking to keep your business working.


SIP trunking allows your business to keep running in a disaster or emergency or balance your call loads between sites during peak hours.

Line Rationalisation

SIP trunking provides the opportunity for line rationalisation and reduces the number of PBXs you need to maintain, while retaining full control of the numbers associated with your business.

Free internal calls

Perfect for medium or large organisations with multiple sites. SIP trunking provides free call termination to UK fixed destinations, between connected sites and international locations.

The Features of SIP Trunking

  • Unlimited Minutes
  • Unlimited Channels
  • Unlimited DDI
  • Call diversions
  • Voicemail
  • Call Recording
  • Call Queues
  • IVR/Auto Attendant Menus

SIP Trunking vs ISDN




Saves up to 50% on line rentals and 25% on calls Expensive


You're in control. Add lines, take them away, split calls Not flexible


Choose how and where you want calls delivered. Make changes instantly Changes take months. dependent on suppliers


Well mapped out and ready for Voice/Data convergence Not future ready, expires in 2025


Handles emergencies with ease. Reroute calls to backup sites in seconds Down Time expected

Frequantly Asked Questions

  • How resilient is SIP trunking?

    SIP trunking is now a mature service enjoyed by thousands of UK organisations and this alone is testimony to the reliability of SIP. For added reassurance while you switch to us, SIP trunking can even be used with existing ISDN connections to ensure the transition goes smoothly.

  • What's the quality like?

    From the moment we connect your SIP trunking service, you will enjoy all the reliability, resilience and quality that comes from SIP trunks.

  • What happens if our internet or power goes down?

    Should disaster happen, you can use SIP trunking to minimise disruption to your business. For example, if your London branch has to close in an emergency, and you need the calls routed to Manchester immediately, SIP Trunks can do this and at no extra charge to you.

  • What if we're moving office?

    Number flexibility with SIP trunking means that you can keep your existing number, even when moving out of the area, saving you costs on printed company literature and stationery whilst maintaining the perception that you still have a presence in the area you’ve moved from. We can easily transfer your old or existing numbers too so that you can avoid expensive Remote Call Forwarding (RCF) or call diversion charges.

    With CLI flexibility you can also decide which number you want to display on a call by call basis – great for contact centres.

  • What if we want to add or remove some of our lines?

    SIP trunks are valuable for businesses with seasonal voice capacity requirements where more lines can be quickly and easily implemented with no long term commitments, for example when running sales campaigns.

    Conversely, if your business has multiple sites with ISDN connections into each, using SIP Trunks you can reduce the number of ISDN connections that your business requires and also reduce the maintenance costs on all of your various PBXs. At the remote sites you are left with just the cost of an IP connection and the handsets that you need and you can then pull all the telephony traffic back into your centralised PBX.

  • What is your pricing?

    Each business infrastructure is different, so pricing is determined by individual solutions.

  • How long does it take to set up SIP trunks?

    SIP Trunking solutions can be set-up within 48 hours.

  • Can I bring my current number with me?

    Yes, Almost all UK telephone numbers can be ported into our system.