Gamma SIP Trunks


SIP Trunking from the UK's leading provider*

Gamma SIP Trunks connect your business 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.


*Illume Report Dec 2015

What is SIP Trunking?

SIP Trunking is our standards based replacement for traditional ISDN. It connects your 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.

"The whole process of switching to Gamma was completely seamless and didn't get in the way of normal working. Now instead of talking to five people at five different companies to get things done, we have one contact at Gamma for everything. It's so much easier and costs us less too."

Sunset + vine logo

Stuart Unwin -
Mentorn Media, Video Arts, Pioneer Productions

Some of the PBX vendors we work with

Solutions for your business

  • Number flexibility

    Gamma SIP Trunks support business relocations by enabling a geographic number to be retained without call forwarding costs. This ensures continuity of business and reduces the costs of having to change company stationery, listings and advertisements. As a leading UK communications provider we can also supply out-of-area geographic number ranges to make your organisation appear local, even without a physical presence. Flexibility with numbering

  • Business-grade voice and internet convergence

    With our SIP Trunks delivered over Gamma Broadband or Gamma Ethernet, you’ll have a high-quality voice and data service from just one connection, making for significant cost savings.

  • Line and PBX estate rationalisation

    For businesses with several locations our SIP trunking service provides ISDN line rationalisation - the ideal way to reduce the number of PBXs requiring maintenance.

  • Business continuity

    Businesses of all sizes need a business continuity plan for their telephony. Our SIP trunks, when combined with our Inbound service, means your callers can always get through. Simply divert published numbers to backup locations or mobile phone - instantly and from anywhere.

  • 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 telephony uptime. Whether you need to keep your 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. In addition, SIP provides free calls between connected sites, including international locations. CallGuard protection from unusual usage is also included free of charge with all of our SIP trunks.

  • Manage your entire inbound number estate through your SIP trunks

    SIP Trunk Call Manager is a brand new solution to the market and encompasses all of the benefits of SIP combined with a unique web-based portal and app service that enables you to take full control of all your inbound numbers, wherever you are, whenever you want.

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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.

Want to know more? Contact us today

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.

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.

  • 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® Lync / Skype for Business, allowing you to directly connect to the platform to make external calls.


SIP benefits table

Hot topics

Hot topic

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Our 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. 

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 you switch to us, SIP trunking 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    Active standby explained

Hot topic

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.  

Hot topic

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.


Hot topic

The Payment Card Industry Data Security Standard (PCI DSS) is the proprietary information security standard defined by the major card companies to help combat fraud and protect consumer card data. Its members include Visa, MasterCard, American Express, Discover and JCB. PCI DSS applies to all organisations that store, process or transmit cardholder information, from any of these members’ cards. The type of annual assessment required varies according to “level”, which is defined according to the volume of payment transactions that are handled.

With 327 controls to consider in total, it is vital to ensure you have them all ticked. The effects of being non-compliant can be disastrous for a business due to the very real financial risk of opportunistic agent fraud and the associated reputational risks. Some of these include:

  • Compromising your customers’ payment data
  • Damage to your brand and reputation
  • Expensive lawsuits
  • Insurance claims
  • Lost customers
  • Payment card user fines
  • Government fines
  • Damaged reputation

Semafone PCI Compliance Gamma SIP

PCI Compliant Gamma SIP Trunking is a flexible and cost-effective telephony solution where you can combine market leading, next-generation telephony with total PCI DSS compliance. It’s quick to install, delivers robust business continuity and supports connections ranging from two channels to an unlimited number. We’re the UK's leading SIP trunking provider, connecting businesses directly into the Gamma network using an IP backbone, enabling full PSTN connectivity while protecting your business from the above risks.

My business issues

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

Business issue

Did you know that Green Flag Breakdown research found that one week of bad weather in 2013 was estimated to have cost UK businesses over £318million and 51 million working hours in lost productivity because business continuity plans hadn't been put in place? Scary statistics. But 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, Gamma SIP Trunks can do this and at no extra charge to you.

Call divert thumbnail    Call divert

See a real example from an insurance company

Business issue

If your business has multiple sites with ISDN connections into each, using Gamma 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. 

See a real example from a Utility company

Business issue

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.

Load sharing thumbnail    Load sharing

See a real example from the Wimbledon Championships

Business issue

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.

See a real example from a top London media company

Business issue

Decide which number you want to display on a call by call basis! Great for contact centres. Use CLI flexibility to present your preferred number on your outbound SIP trunk calls.

CLI flexibility thumbnail    CLI Flexibility

See a real example from the Wimbledon Championships