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SIP trunking is the replacement for traditional ISDN

SIP Trunks are standards-based and connect your Phone System (PBX) to the Outside World (PSTN) via an Internet connection.

SIP trunking services are typically less costly per channel than the ISDN it replaces and is more flexible in how and where geographic telephone numbers can be used. It’s quick 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.

Our SIP trunks work seamlessly with each of the leading IP PBX brands in the UK market. Where you do not have an IP compatible system we can supply ISDN - SIP gateways.

Any business with a PBX can switch to our SIP trunking service and immediately benefit from a more flexible, typically less expensive and more resilient phone service.

Don’t have a PBX? Why not consider our hosted phone system - IC-talk

Frequently Asked Questions - FAQs

SIP Trunks being delivered on common infrastructure and partial public infrastructure can save money on both rentals and call costs of between 25% & 50% typically...

Cost is not however what is driving adoption with many choosing to increase features, flexibility and resilience over cost savings to make their business better equipped.

Sorry this is a myth, carriers have a 'settlement' fee and it is like an old boys club but on the plus side it enforces integrity and some quality levels. Moving a call from a phone line to SIP is moving it to data and this still costs and needs resources.

All that said we do offer on term contracts free UK landline and mobile calls...

SIP trunking is now the largest medium having overtaken ISDN and is a mature service. 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 add layers of quality and control which allows us to deliver high levels of diversity and failover technically in excess of the ISDN services it has replaced. It is also designed for disaster recovery scenarios and has flexible call routing and redirection rules that far exceed the legacy ISDN network.

Depending upon your phone system it is either the same or better.

The system is constantly monitored and measured using an industry standard mechanism and our SIP trunks consistently exceed the quality that you would have from ISDN. Being not constrained like the previous generations, with SIP you can actually switch to far higher HD qualities and have sound like never before.

Quality is not a question it is a plus point to move...

SIP trunk services have been designed with failover in mind, options are varied and available where by an individual DDI / phone number various alternative routing can be performed. Be it to another office, home, computer or mobile you can always be available.

As SIP trunks are not geographically constrained this is not an issue at all, just get your new office connected to the Internet and point your calls to the new site / system.

A word of Note:

Check your proposed new premises has good Internet connectivity prior to committing as this is a pre-requisite of the service. IC can do this for you and your privacy is paramount, we do this often for companies for acquisitions, mergers and re-locations which may be commercially sensitive.

Short answer is very, providing you have sufficient capacity on your connection to the premises or phone system (you need about 100Kb/s per concurrent phone call) then you can flex the number of channels as required.

You should allow at least 100Kb/s per concurrent call you want to have and as a general rule never exceed 80% of your connections total capacity.


While you can use Broadband services to run your SIP trunks they are by definition usually shared connections and subject to contention and variable speeds.

IC can advise and supply suitable connections for maximum call quality and stability.

Contact us for more details...

For more information or pricing please contact us or log in to myIC

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Tel.    01782 667788
Sales 01782 667700

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