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With Gamma SIP trunking from TMB, your business is connected to the Public Telephone Network (PTSN) using Voice over IP (VoIP) instead of traditional ISDN or analogue lines.

This delivers several cost saving and productivity benefits for your business:

  • Reduce your telecoms expenditure

With calls charged on a per-user basis and simpler pricing structure for domestic and international calls, you can expect to significantly reduce your monthly spend and predict your bills with greater certainty. Save up to 50% on line rental and 25% on call costs.


  • Improve collaboration with remote teams

With SIP trunking, you can connect your employees’ mobile devices via VoIP secure apps, so that everyone in your company can stay connected to your on-premise phone systems when out of the office.


  • Scale-up with ease

SIP trunking allows you to add additional capacity to your infrastructure simply by connecting devices to your data connection, so off-site workers can be easily contacted via a single dedicated phone number and extension.



  • Save money on hardware

With SIP trunking, you don’t need to invest vast sums in additional hardware every time you expand your telephony system. TMB can add services or additional phone lines for an affordable price and, because our contracts are designed to be flexible, altering your monthly commitment is an inexpensive and easy option.


  • Improve reliability

Unlike conventional network connections, SIP trunking isn’t prone to the frustrating service interruptions that can occur when cables become damaged or equipment malfunctions. Should a problem arise with your VoIP connection, disaster recovery and business continuity solutions can be triggered to ensure that service is maintained and not a single call is lost.

SIP Trunking

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Making the switch from ISDN to SIP trunking

With ISDN set to become a legacy product by 2025, SIP trunking is at the forefront of modern business telephony, offering irresistible benefits for businesses who recognise communication as a key driver in their long-term profitability and success.

TMB and Gamma – a winning partnership for all your telecoms requirements

As an approved Gamma supplier, TMB can support you to switch your PBX to SIP trunking, for a more flexible, resilient, and cheaper business phone service.

As a specialist B2B communications provider and the UK’s leading SIP provider, Gamma has unrivalled industry experience of facilitating cost-effective solutions that deliver exceptional service quality for more competitive prices.

  • Business-grade voice and internet on a single connection.
  • Business continuity so your callers will always be able to get through.
  • Line and PBX estate rationalisation for businesses with multiple sites, to reduce maintenance.
  • Free calls to UK fixed line numbers and connected sites worldwide.
  • Number flexibility to reduce the cost of business relocations.
  • CallGuard protection against phone hacking and abuse.


Compatible with all leading IP PBX brands in the UK, Gamma SIP trunking is the most cost-effective and logical alternative to ISDN. With ISDN due to be discontinued from 2025, now is the best time to switch to SIP trunks to give you the reassurance you need that your business operations will continue to operate seamlessly in the years ahead.

Request a quote

If your business is facing an ISDN black hole when existing network connections are switched off, Gamma SIP trunking can deliver a more reliable, cost-effective, and scalable solution. To find out more or to request a free, no-obligation quotation, please call TMB on 0333 016 2203. 

If you would like to learn more about our services, simply click the button below to request a callback.
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