Business grade SIP trunks

Utilise SIP trunks across our Tier 1 carrier network to benefit from maximised resilience and free calls. Empower your business with the flexibility of VoIP.

Reliable SIP trunks for your business calls


Scalability to grow with you


Free calls across our SIP Trunks


Use any geographical number


Multiple options of SIP Disaster Recovery


All modern PBX supported


Supported by SIP designed data connections

Business grade SIP Trunks

Take advantage of our low cost SIP Trunk line rental and call charges which are compatible with all types of telephone systems that can use SIP Trunks.

Number Flexibility

Our SIP trunks allow you to relocate your business without the call diversion costs associated with changing to a new geographic number. This not only provides continuity of service, yet removes the costs associated with changing numbers on literature, stationery, business listings etc. Equally we can provide any 01/02 geographic number into your SIP account, providing your business with a presence anywhere across the UK.

Continuity of Service

Combining our SIP trunks with our Inbound platform will offer your business a secondary level of disaster recovery. DR can be added within the SIP setup to enable an instant divert to a secondary destination if required.

Future Proof and Rationalisation

With BT withdrawing ISDN services in 2025, SIP trunks is a future proof alternative to any ISDN30e or ISDN2e solution. For businesses with multiple sites SIP trunks provides ISDN rationalisation, which is a great way to reduce the number of phone systems requiring maintenance.

Free UK Calls and Fraud Prevention

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. We also provide fraud protection and alerting at no cost with all our SIP trunks.

SIP Trunks in summary

Choose your own SIP Number

Regardless of geographical location

Port Existing Numbers

From ISDN or PSTN lines

Managed Connectivity

Use our Assured Voice or Ethernet to ensure QoS

DR Ready

Opt for a backup circuit for your SIP trunks

Why you should use our Data connections for SIP

Assured IP is a voice only broadband connection created for SIP trunks. These connections are 1:1 contended, have QoS, and prioritise voice traffic. Our SLA includes a target service availability of 99.95% from the core network.
Converged Broadband – is a voice and data circuit, allowing SIP trunks and web browsing on a single connection. They are provided with QoS using the Cisco 800 series routers, and are backed by a performance SLA, ensuring clarity in voice on our SIP trunks.

All our managed data connections for SIP include a managed Cisco router.

Benefits of our SIP Offering Include:

  • FREE calls Free calls between SIP sites
  • Low Rental Low SIP trunk rental per month inclusive of 01, 02 & 03 calls
  • Free Mobiles calls 2,000 minutes of free mobile calls per SIP trunk
  • Scalable Fully scalable on a per SIP channel basis, unlike ISDN
  • Low initial cost Minimum order is only 2 SIP Trunks/Lines
  • Any UK range Flexible number ranges on our SIP service
  • Quick setup Easy to order and provision to your Equipment and integration strengths
  • Any Internet Technology SIP is available over LLU/ADSL, EFM or Ethernet
  • Emergency Services Offers emergency services support
  • Voice Internet Circuits SIP designed data connections offering QoS, including Assured & Converged

SIP stands for session Initiation protocol which is the protocol that controls setting up the call and tearing it back down again.

A SIP trunk is a virtual telephony line that connects your office to the outside world using a data connection instead of an ISDN or analogue phone line. SIP trunks carry your voice calls like an ISDN circuit would, generally at a lower cost. SIP calls between two SIP enabled sites are zero cost as the call remains on-net.


A SIP Trunk is carried across your existing data network. This removes the requirement to have expensive BT Openreach line rentals. SIP trunks are more flexible than normal PSTN lines. They allow you to present multiple numbers to your customers, and the number your business uses day-to-day is not subject to your location – it can be any number.


Whilst you can run SIP Trunks on any data connection we recommend using one of our designed data circuits, either assured IP, converged or Ethernet. SIP calls require bandwidth, and if you do not have sufficient bandwidth on your existing data circuit it is likely you will experience disconnected calls and jitter.


Providing you choose the right partner, YES. SIP calls can become problematic if:

  • the data connection cannot support the number of concurrent calls
  • the SIP network is not reliable with the necessary failover equipment
  • the end user equipment is not up to date to support your SIP trunks

We ensure that our solution will work within your environment before we put pen to paper. We offer data connections that suit your expansion rates, our SIP partner is the largest provider of VoIP in the UK, and should your phone system not be up to the task we can recommend our hosted solution, Horizon.


Generally the answer would be YES. SIP trunks are cheaper than ISDN30e and ISDN2e line rental, and call costs are lower when utilising SIP trunks, including zero cost site-to-site calls. However what is sometimes overlooked is the internet connectivity to deliver your SIP calls. As mentioned in the SIP reliability question, to try and push SIP calls across a low-end data connection could have a disastrous impact on your business.


If your phone system is new, it is likely you will have the capabilities to connect SIP trunks without too much fuss or cost. What you may need is an additional SIP card or licenses which you will need to obtain from your phone system supplier or Maintenance Company.
If your phone system cannot support SIP then now may be the time to look at a hosted solution. We have 1000’s of users currently enjoying the benefits of Horizon today.


In most cases, YES. Geographic number porting is quite simple and painless. We can port your geographic number from most Tier 1 carrier networks. 95% of the time customers port their geographic number from ISDN or analogue BT Openreach lines to our SIP trunking solution.


Ethernet Access

Use our Ethernet checker, providing instant pricing for speeds up to 1GB with Disaster Recovery failover options, to your offices in less than 60 seconds.

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Inbound Numbers

Choose a non-geographic 08 or 03 number from our extensive selection of numbers. Hosted on our Inbound platform changing call plans and access to live reports are standard.

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SIP Trunks

Competitively priced inclusive UK landline and mobile minutes are provided with all our SIP services. Utilising the largest UK SIP networks our platform is inherently resilient.

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Hosted Phones

A seamless cloud based plug and play hosted phone system. Ideal for SoHo to Enterprise, Horizon offers a feature rich low cost alternative to a traditional phone system.

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Telecoms Audit

Did you know over 54% of UK businesses are charged for services they no longer require? Take advantage of our no-obligation audit where we’ll highlight obsolete services and reduce costs.

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