Discover the power of
SIP Trunking


SIP Trunking

Connexin SIP trunking offers a more flexible and lower-cost alternative to ISDN for inbound and outbound calls. As a replacement for traditional ISDN, SIP trunks connect your PBX to our national telephony network via broadband, ethernet or private circuit rather than over old copper phone lines.

Compared to ISDN, our SIP trunking service is cheaper, scalable and more flexible in how and where telephone numbers can be used. SIP trunks are also quicker to install, provision and deliver 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 Trunking


per SIP Trunk per month
  • 4000 FREE calling minutes to UK 01, 02, 03 and mobile
  • Competitive call rates
  • 9 – 5 UK based support

£100.00 setup fee applies.

SIP Trunk

£10 per channel

£8 per channel

Add as many additional channels as you need to your SIP Trunk. The more channels you have on your SIP Trunk, the more simultaneous calls you make and receive. Each additional channel comes with an additional 4000 FREE calling minutes to UK 01, 02, 03 and mobiles.

UK Direct
Dial Numbers

£10 per DDI

£2.50 per DDI

Additional UK DDI numbers can be added to your SIP Trunk. With our SIP Trunking product, you can add as many numbers as you like.

SIP Trunk
Call Manager

£10 per endpoint

£40 per endpoint

SIP Trunk Call Manager provides you with all the benefits of SIP Trunks together with a centralised inbound call management service with a host of features, accessed through an easy-to-use web portal and mobile app.

More about the SIP Trunk free calling minutes

Free calling minutes are to UK 01, 02, 03 landline numbers and UK mobile numbers only. All other calls are charged at the standard advertised rates. A minimum contract term of 12-months applies unless otherwise stated. All prices shown exclude VAT. For more information, please see our full terms and conditions.

Speak to our experienced voice specialists today

By submitting this form, you are providing your consent for Connexin to contact you to discuss your requirements now and offers from time to time. You can opt out at any time if you change your mind. To view our privacy policy please click here.

Some of the PBX vendors we work with


Save money

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

Perfect for medium or large organisations with multiple sites, not only will you save on your line rental and call costs, but you will also get free internal calls within your organisation and a whole host of great features.

Scale whenever

SIP trunking is 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.

Business continuity

SIP trunking can handle emergencies easily. They are inherently disaster recovery/business continuity ready, letting you reroute calls to an alternative location quickly and easily.

Number flexibility

SIP Trunkinng support business relocations by enabling a geographic number to be retained without call forwarding costs. We can also supply out-of-area geographic number ranges to make your organisation appear local, even without a physical presence.

Fraud protection

Hacking and abuse of business telephony are becoming as big as credit card fraud. Our SIP Trunking comes standard with fraud protection by monitoring unusual call usage.


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.

With Connexin, we identify and fix issues faster, through our advanced monitoring and diagnostic tools. It is 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 Connexin SIP Trunks.

What’s the quality like?

From the moment your SIP trunks are connected, 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.

What happens if our internet or power goes down?

Should a 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, Connexin SIP Trunking 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 more lines?

SIP trunks are valuable for businesses with seasonal voice capacity requirements where more lines can be quickly and easily implemented, for example when running sales campaigns.

Conversely, if your business has multiple sites with ISDN connections into each, using Connexin 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.

Does SIP work with other business networks and applications?

Connexin SIP Trunking is 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 Connexin 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.

Interested in SIP Trunking?

Speak to one of our specialists on 01482 363738.