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SIP Trunking

SIP Trunking

Multiple numbers, multiple benefits

You can’t be in several places at once - but with SIP Trunks, your business can. Allowing you to channel multiple numbers from different exchanges into one office, you can have London, Glasgow and Bristol numbers all answered in Birmingham.

And that’s just one of the advantages of moving your telephone lines to Spitfire SIP Trunking.

You’ll also benefit from lower call costs (saving more than 80% compared with BT Retail), exceptional call quality supported by Voice Approved Internet Circuits, and a yearly saving of up to £3000 against ISDN30e rental.

Business SIP Trunks – High Reliability UK SIP Trunking


From £4 per SIP Trunk per month


If you need the flexibility and control of your own phone system – and either already have a phone system or are happy to buy, run and manage the phone system yourself – SIP Trunks are the right choice for you.


Trust Spitfire for superior SIP Trunking

  • Business SIP Trunks from just £4 per month
  • Guaranteed call quality via Spitfire Ethernet or Voice Approved SDSLM
  • Keep your existing phone number forever, wherever you move
  • Service implemented on our own core network infrastructure
  • Flexible options for providing backup to ISDN lines
  • Award-winning support

Cost Comparison – Spitfire SIP trunks and BT Retail ISDN30e


10 ISDN30e lines and 100 DDI numbers, Spitfire SIP Trunks are 53% less expensive – with a wide range of back up options:


  • One year BT Retail ISDN30e with 10 channels and 100 DDI quota plus CLIP – £212.31 per month.
  • Spitfire SIPStream® SDSL 2Mb 1:1with back-up ADSL circuit, 10 SIP trunks and 100 DDIs – £99 per month.
  • Saving over £110 per month, with guaranteed ISDN30e equivalent quality.


30 ISDN30e lines and 200 DDI numbers, Spitfire SIP Trunks are 47% less expensive – with a wide range of back up options:


  • One year BT Retail ISDN30e with 30 channels and 200 DDI quota plus CLIP – £602.06 per month.
  • Spitfire 3Mb Ethernet circuit, 30 SIP trunks and 200 DDIs – £320 per month.
  • Saving over £275 per month, with guaranteed ISDN30e equivalent quality.

More About SIP Trunking


There are a three key elements to delivering ISDN30e quality SIP Trunking for businesses: A SIP compatible Phone System or Gateway, an Internet connection designed for Voice, and the ability to terminate SIP calls onto the standard phone network.


Spitfire are one of the few SIP Trunking providers able to offer a complete end-to-end SIP Trunking service.


Indeed, Spitfire SIP Trunks are a genuine alternative to ISDN30e – with us providing a managed service covering the IP connectivity, SIP Trunks and number management – exactly the same as with ISDN30e. We take responsibility from day one for delivering a robust, business-class SIP Trunking solution.


What’s more, we also provide SIP Trunks through another leading UK Wholesale Provider, Gamma Telecom. We use these wholesale SIP Trunks in situations where a customer wishes to use a non-Spitfire circuit, or where Spitfire SIP Trunks are not tested with a particular phone system or application. Effectively having access to two SIP networks allows you to have two separate SIP Trunk services all managed by Spitfire. These non-Spitfire SIP Trunks, provided by Gamma Telecom, are sometimes referred to as Off-Net SIP Trunks.


See a more detailed explanation of SIP Trunks here

Spitfire SIP Trunks – more benefits and savings


  • Spitfire runs its own core network infrastructure to implement our SIP Trunk service.
  • We can provide telephone numbers from geographic areas all over the UK and route them to your SIP service, enabling you to have a virtual office anywhere.
  • Our SIP trunking has flexible options for providing backup to ISDN lines and vice-versa , and further options to forwarding to mobiles/home numbers.
  • Spitfire can provide all the components necessary to connect your telephone system via SIP Trunks including quality IP access and gateways, including on site engineering.
  • We take responsibility for delivering your SIP Trunking solution from the day you place your order, including the circuit, numbering, back up and engineering.
  • With our dedicated test facility we have tested our service with a wide range of manufacturers SIP devices.


Ready to make the switch to SIP Trunking? Make the call. Our expert consultants are available on 0800 319 6363.

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