Gamma SIP Trunks

SIP trunking from one of the UK’s leading providers

Our SIP trunking service connects your customers' businesses with our nationwide network, gives access to the PSTN and provides a more flexible and lower cost alternative to ISDN for inbound and outbound voice calls..

Intro to SIP trunks for channel partners video

An introduction to Gamma SIP Trunks for Channel Partners 

Some of the PBX vendors we work with

Give your customers unparalleled flexibility with SIP trunking from Gamma

What is a SIP trunk?

SIP (or Session Initiation Protocol) - also known as SIP trunking - is our market-leading and cost-effective replacement for traditional ISDN.  It connects your customers' PBX to the PSTN via broadband, Ethernet or private circuit into our national network. Our SIP trunks work seamlessly with each of the leading IP PBX brands in the UK market.


SIP cloud icon

Can I have SIP Trunking in my business?

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 v ISDN cost calculator right now and see for yourself. Don't have a PBX? Consider our Hosted Horizon phone.

SIP migrations guide

Product family

The benefits of Gamma SIP Trunks

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. 

Are you leveraging the
MS Lync opportunity? Visit our dedicated SIP with Lync website

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..

  • Lower cost
    First and foremost SIP is significantly less costly than ISDN. It offers your customers the opportunity to make real operational cost savings through free calls to UK 01, 02, 03 and mobile number ranges, whilst at the same time improving service flexibility
  • It enables line and PBX estate rationalisation
    For businesses with multiple sites, our SIP trunking service provides ISDN line rationalisation options and they are the ideal way to reduce the number of PBXs that require maintaining, whilst your customer retains full control of the numbers associated with their business
  • It offers number flexibility
    A great feature of Gamma SIP Trunks is the ability to support business relocations by enabling a geographic number to be retained, without incurring any ongoing call forwarding costs. This not only ensures continuity of business, it also reduces the cost impact associated with having to change company stationery, directory entries and advertisements. As a leading UK communications provider we can also supply our SIP trunking customers with out-of-area geographic number ranges for customers, who for example wish to appear local, even if they don’t have a local physical presence
  • It's business-grade voice and internet convergence
    With Gamma SIP Trunks delivered over Gamma Broadband or Gamma Ethernet, your customers can have a high-quality voice and data service from just one connection and they’ll make significant cost savings
  • Business continuity comes as standard
    Businesses of all sizes need a business continuity plan for their telephony. Our SIP trunks, when combined with our Inbound service, means your customers' callers can always get through. Simply divert published numbers to backup locations or mobile phone - instantly and from anywhere
  • It offers affordable resilience
    If you’ve ever had to deal with a service outage you’ll know first hand that speed of response is key. Our active/standby and load sharing designs are engineered to cope with any situation so maintaining your customers' telephony uptime. Whether your customers need to keep their businesses running in an emergency without the high cost of call forwarding or simply need to balance call loadings between sites during peak, Gamma SIP Trunks will provide a business grade solution
  • Free UK calls and fraud protection
    Our SIP trunking service provides free call termination to UK fixed destinations, including 01, 02 and 03 number ranges, allowing you to focus on the service benefits rather than a straight pricing discussion. If you prefer it, you can set the price your customer pays, creating a uniquely-differentiated proposition, which gives you a massive edge. In addition, SIP provides free internal calls between connected sites (including international)
  • It's reliable
    Horizon is another reliable service from Gamma and for complete peace of mind we provide a support wrap that includes training, number porting, provisioning and the sort of 24/7 UK-based assistance you’d expect from the leaders in IP telephony

SIP benefits table

Hot topics

Hot topic

Microsoft Lync

Through a clever yet simple integration, Gamma SIP Trunks can extend unified communications beyond the office environment by connecting Lync™ to the public network. Combining the functionality of Microsoft® Lync™ with the cost-savings and business-grade resilience of Gamma SIP trunking solutions offers you and your customers lots of benefits.

Are you leveraging the
MS Lync opportunity? Visit our dedicated SIP with Lync website

Hot topic

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 your customers switch to us, they can even be used with 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 Gamma SIP Trunks.

Active standby explained video thumbnail     Active standby explained

Hot topic

Our free fraud protection service limits exposure for both you and your customers, to fraudulent activity from endpoints that have fallen victim to hacking or excessive unauthorised call spends.

This free fraud protection service gives you:

  • Pre-set individual call limits against specific endpoints or users
  • Automatic call barring where thresholds are breached
  • Exclusive access through the Gamma Portal so that you have direct control and without requiring input from Gamma 
  • Peace of mind that you will not be responsible for any fraudulent over-spend above the configured threshold limit

Fraud management for SIP trunks video thumbnail     Fraud managment for SIP Trunks

Hot topic

From the moment we connect their SIP trunking service, your customer will enjoy all the reliability, resilience and quality that comes from being on the UK's fourth largest network. 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.  

Quality is assured through :

  • Extensive monitoring of all elements and metrics within the call path both TDM and IP including but not limited to, Post Dial Delay (PDD), Answer to Seize Ratio (ASR), Network Efficiency Ratio (NER), Mean Opinion Score (MOS), Perceptual Analysis of Speech Quality (PESQ) Score, Call Closure and Error codes for C7 and SIP signalling, Jitter, Latency, Packet Loss, Trunk and Circuit occupancy, uptime and trends
  • Proactive call testing and analysis for all platforms and services
  • Appropriate and timely alerts of potential issues and ‘hot spots’ to our 24x7 Network Operations Centre
  • Review of external and internal reports including customer feedback via support desks
  • Strict Change Control and Release Management process aligned with our suppliers and carrier partners to prevent related quality or service issues
  • Oversight through a monthly Quality Steering Group meeting chaired by our CEO that includes input output from our regular Platform Service Reviews, Capacity Management, Information Security and Business Continuity forums
Hot topic

Janet company logo

We’re a Janet-connected partner with a direct, geographically diverse interconnect to provide voice services in the form of Gamma SIP Trunks to the Janet community. Janet is the network dedicated to the needs of research and education in the UK, connecting the UK’s research and education institutions to each other, as well as to the rest of the world. 

Solving business issues

Here are just some of the current business issues we encounter with our customers where we can really help.

Business issue

If your customer’s office has to be temporarily relocated in an emergency, this can quickly and cost-effectively be achieved with Gamma SIP Trunks. Providing your customers with the additional business continuity benefits that come as standard with our SIP service helps to create stickier relationships and increase retention. 

Call divert video thumbnail    Call divert

Business issue

For businesses with multiple sites, SIP trunking provides ISDN line rationalisation options and reduces the number of PBXs that require maintaining - all with full control over the numbers associated with your customer’s business.

Business issue

Gamma SIP Trunks are valuable for businesses with seasonal voice capacity requirements where more lines need to be quickly and easily implemented with no long-term commitments, for example when running sales campaigns or during major sports or entertainment events.

Unlike ISDN, SIP trunks are a highly cost-effective system that can be scaled up and down according to the requirement enabling more effective use of IT team resources by making the provisioning of new users with voice and data systems quick and easy.

Load sharing video thumbnail    Load sharing   Sporting event case study

Business issue

The perfect solution for businesses that are starting up, growing or in fixed-term leases; our SIP trunks enable seamless routing of geographic and non-geographic numbers, to any location. This allows your customers to move office and keep their same geographic number without incurring any ongoing call-forwarding costs or costs associated with producing new company stationery, adverts or directory listings.

Business issue

With Gamma SIP Trunks delivered over Gamma Broadband or Gamma Ethernet, you can have a high-quality voice and data service all over one connection, giving you significant cost savings.