Gamma SIP Trunks

SIP trunking from the UK’s leading provider*


* Illume Report Dec 2015

About Gamma SIP Trunks

Gamma SIP Trunks connect 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.

The benefits of Gamma SIP Trunks

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 numbers, whilst at the same time improving service flexibility.

Line and PBX estate rationalisation

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.

Number Flexibility

Gamma SIP Trunks support business relocations by enabling a geographic number to be kept 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. We can also supply SIP trunking 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.

Business-grade voice and data 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 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, load sharing and resilience designs are engineered to cope with any situation and maintain 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, mobile calls and fraud protection

Our SIP trunking service provides free call termination to UK fixed destinations, including 01, 02 and 03 number ranges, as well as mobile calls, 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.

Would you like to know more? Get in touch today

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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.

Which customers is SIP suitable for?

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. For customers that don’t have a PBX, consider our Hosted Horizon phone.

How resilient is SIP?

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, SIP trunks 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 the reliability of our service that’s helped us win many major UK fixed line network awards in recent years and one of the reasons more and more businesses are choosing Gamma SIP Trunks.

How does SIP compare to ISDN?

Savings Saves up to 50% on line rentals and 25% on calls Expensive
Flexibility You’re in control. Add lines, take them away, split calls – it’s up to you Sorry, can’t do flexible
Control Choose how and where you want calls delivered. Make changes instantly Changes take months. At the mercy of suppliers
Future Well mapped out and ready for Voice/Data convergence Going nowhere fast
Contingency Handles emergencies with ease. Reroute calls to backup sites in seconds Hope nothing bad happens

Is SIP secure?

Absolutely!  A properly configured and managed SIP service will give you the service assurance you are looking for:

  • We only employ IP authentication.
  • We can build private layer 2 VLANS to customer devices that support RFC 1918 addressing. On this basis the endpoints cannot be seen from the public Internet.
  • Traffic patterns on the Session Border Controller (SBC) are monitored for anomalous behaviour and appropriate alerts deployed
  • Rate and channel restrictions are place on all endpoints to ensure that the SBC cannot be overloaded.
  • All SBC’s are deployed in fully secure premises
  • Gamma is fully compliant with the Information Security Standard ISO27001 and the Business Continuity standard ISO22301
  • SIP trunking SBCs and Portal are penetration tested by professional 3rd party consultants to offer assurance that the security is fully effective

In addition, our free fraud protection service limits exposure 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, without requiring input from Gamma
  • Peace of mind that you will not be responsible for any fraudulent over-spend above the configured threshold limit

How does Gamma ensure quality?

From the moment we connect their SIP trunking service, your customer will enjoy all the reliability, resilience and quality that comes from being one of the UK’s largest providers of voice services and voice applications.

Quality is assured through:

  • Proactive monitoring and management of quality of service functions across our entire network 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 24×7 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

Some of the PBX vendors we work with

Solving business issues

Here are just some of the current business issues end customers are facing that Gamma SIP Trunks can help address:

Business Continuity

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.

Site rationalisation

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.

SIP for seasonality

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 expected busy periods like 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.

Moving office

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.

Voice and internet convergence

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.

SIP Trunk Call Manager

Enable your customers to manage their entire inbound number estate through their SIP trunks

SIP Trunk Call Manager provides all the features and benefits of Gamma SIP Trunks together with centralised call control. This includes our market-leading call bundles and the only fraud management tool that protects you and your customers by enabling them to set spend limits. SIP Trunk Call Manager offers a powerful business continuity solution, giving your customers the ability to manage their number estate and all aspects of their inbound calls.

Visit our SIP Trunk Call Manager page to find out more.

Gamma SIP Trunks with Skype for Business

Gamma SIP Trunks are integration-tested and qualified by Microsoft to interoperate with Skype for Business (previously Microsoft® Lync). This enables direct connection of SIP trunks to Skype for Business for external calls from the platform, providing a seamless experience and making it an ideal solution for any organisation that’s looking at implementing Skype for Business or already uses it.

SIP Trunking for cloud platforms

Connect your cloud platform to the UK Telephony Network (PSTN) with one of the UK’s largest voice infrastructure providers

Click here to find out more.

SIP in the Education sector (Janet network)

We’re a Janet-connected partner with a direct, geographically diverse interconnect to provide 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.

Making the move from ISDN to SIP

Introduce your customers to a better alternative to traditional telecoms

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Have you seen our other products?

Horizon is a hosted phone service that provides an extensive range of fixed and mobile telephony capabilities via an easy-to-use web portal.

gamma sip trunking

Free Fraud Management

Gamma’s fraud management services protect you and your customers from fraudulent activity from endpoints that have fallen victim to hacking or excessive unauthorised call spends. Fraud Management is free with Horizon and our Gamma SIP Trunks and 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, under your 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


Exactive talks about Gamma SIP Trunks



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