SIP Trunking

Protect your existing investment or refresh your telephony with Claranet

SIP Trunking connects your existing private branch exchange (PBX) to the national public switched telephone network (PSTN) using an IP connection. This provides a more flexible and low cost replacement to ISDN connections into the PBX. Alternatively, if you are looking to refresh your telephone system, see our Hosted Voice services.

Why choose Claranet as your SIP trunk service provider?

  • SIP trunk expert advice included
  • UK support 24x7x365 included
  • Get the most from existing hardware
  • Consolidate suppliers and save time and cost

Why choose Claranet for Communications?

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How to survive the software revolution

How to survive the software revolution

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Watch the Robinsons case study video

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Flexible and low cost replacement for ISDN lines

diagram for sip trunking process

SIP Trunking overview

  • Private IP telephony service that doesn’t touch the public internet
  • Geographic numbers
  • Flex the number of channels as your requirements change
  • Foundations of a future-proof communications solution
  • Stability and confidence through market leading partnership
  • 24x7x365 UK support
  • 99.987% service availability

Download service overview PDF

How we work with you


Our experts can advise you how our telephony options can be tailored to your business needs


Working with Claranet removes the burden of project managing and carrying out the installation of your SIP Trunking service yourself, saving you time.


We take care of the ongoing 24x7 management of your service. However, you retain the control you need with access to around the clock UK support.


We work with you to ensure your service continually meets your needs.

SIP Trunking business benefits

Business Benefit of cost effectiveness

Reduce costs

By cutting your existing call plan and lines with our competitive rates and consolidating your telephony and data infrastructure

Business Benefits of increased functionality

More functionality

Get more out of your existing telephony hardware

Business Benefits of availability, resilience and reliability

Enhance resilience

Built-in business continuity options

Related Services

Managed Networks and MPLS

Questions? Get in contact with us

Make a sales enquiry

Please fill out the form below with your sales enquiry and we'll get back to you as soon as possible. If you are looking for technical support please email

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We aim to respond to all email enquiries within 5 working days, but we usually respond within 24 hours.

Speak to a member of the team

Please give us a call on 0207 685 8000 between 09:00 - 17:30 Monday to Friday to speak with one of the sales team.

For small business enquiries, please call Claranet SOHO on 0800 640 8009

Looking for technical support? Our UK support team are available 24x7x365 to help on 0330 390 0500


  • Can I keep my existing PBX?

    Yes, provided it is one that is on our approved pre-tested list. Older PBXs may need an additional piece of equipment (either a SBC or gateway) to connect to the SIP trunking service. It may also be necessary to upgrade your PBX to the most recent firmware version.

  • What infrastructure do I need in place?

    A Claranet MPLS connection capable of carrying the voice channels required for your PBX. Additional hardware may be required.

  • Can I pair this with an existing solution?

    Yes, it is possible to mix SIP trunking from Claranet with traditional ISDN connectivity for resilience purposes.