SIP Trunking

Our UK SIP trunk solutions offer a more flexible and lower cost alternative to ISDN for inbound and outbound voice calls.

Upgrade your ISDN today! Call us now on 0330 024 2003.

UK SIP trunk solutions | Focus Group | ISDN alternative
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Our Voice experts are here to help. Give us a call on 0330 024 2003 or request a call back and our team will take care of everything you need.

A cost-effective alternative to ISDN that provides flexibility and continuity

SIP trunking is rapidly replacing ISDN services and Focus Group is the UK's leading SIP trunk solution provider. Our SIP trunks connect your site directly into the Focus network via an IP connection to carry and terminate your inbound and outbound voice calls across the public telephone network.

SIP Trunks provide a highly-flexible alternative to ISDN and are compatible with all the leading IP PBX brands in the UK market, giving you peace of mind that your PBX hardware works with the network service.

Call Focus Group today for a tailored quote on 0330 024 2003











Extension Numbers

Installation Price

Business Continuity Support

Competitive Call Rates

No minimum Call Charge

No Connection Fee or Call Connection

2 - 50

Unlimited DDI's

Variable - up to £275.00






Unlimited DDI's

Variable up to £120.00






Focus Group SIP Trunks are suitable for any size of business from small businesses to large enterprises and government organisations that currently have a PBX, unified communications solution or key system.

UK SIP Trunk solutions | Focus Group

What is Focus SIP Trunks?

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 UK SIP trunking solutions are 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 delivers extremely robust business continuity as standard.

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.

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

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.

Try our SIP vs ISDN cost calculator right now and see for yourself.

Don't have a PBX? Why not consider our hosted phone system - Horizon.

Why upgrade to SIP?

  • Save money on call costs and line rental
    SIP delivers less costly, more reliable connectivity than ISDN over an IP connection. It can save up to 50% on line rentals and 25% or more on call costs.
  • Free internal calls and great features
    Perfect for medium or large organisations with multiple sites, not only will you save on your line rental and call costs, but you'll get free internal calls within your organisation and a whole host of great features.
  • Scale up and down when you want
    SIP trunks are ideal if you are moving, upsizing or downsizing and want to keep your existing numbers. Scale up lines during busy periods and back down again afterwards. You can add lines, take them away, split calls at any time. You are always in control.
  • Built-in Business Continuity
    SIP trunks can handle emergencies easily. They are inherently disaster recovery / business continuity ready, letting you reroute calls to an alternative location quickly and easily.
  • Compatible with Skype® for Business
    Our SIP trunks are integration tested and approved to interoperate with Microsoft Skype® for Business, allowing you to directly connect to the platform to make external calls.

Why Focus Group choose SIP Trunks?

UK SIP trunk resilience

How resilient is SIP trunking?

SIP trunking is now a mature service used successfully by thousands of UK organisations, which is testimony to the reliability of SIP. For added reassurance when you switch to us, SIP trunking can be used alongside existing ISDN connections to ensure the transition goes smoothly.

Owning our own national network means we can identify and fix issues faster, through our advanced monitoring and diagnostic tools. It's a combination which has helped us win many major UK Fixed Line Network awards in recent years and one of the reasons more and more businesses are specifying SIP Trunks.

Internet power outage

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.

Add or remove lines

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.

UK SIP trunk quality

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 working with the UK's leading SIP trunk provider. We proactively monitor and manage quality of service across our entire network - it's the underlying network quality that makes a real difference to SIP trunking. And as a consequence we are able to support both G.729 or G.711 codecs.

Moving offices

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.

SIP network applications

Does SIP work with other business networks and applications?

SIP Trunks are integration tested and approved to interoperate with Skype® for Business, allowing you to directly connect to the platform to make external calls.

We're also a Janet-connected partner with an interconnect to provide voice services through SIP Trunks to the Janet community. Janet is the network dedicated to the needs of research and education in the UK, connecting institutions to each other, as well as to the rest of the world.

Focus Horizon

Why not upgrade to a hosted solution?

Horizon is a hosted business telephone service that resides in the cloud rather than your office. It provides an extensive range of fixed and mobile telephony capabilities accessed through an easy-to-use web portal. The service allows you, the administrator, to easily manage your environment whilst enabling your employees to maximise their productivity.


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