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What are SIP Trunks? A Brief Guide | Gradwell

SIP Trunks

When it comes to communications, businesses are always on the lookout for ways to cut costs and future-proof their organisation. As part of this, one important concept to understand is SIP Trunking.

An Introduction to SIP Trunking

When it comes to business communications, professionals are always on the lookout for ways to become more efficient, cut costs and future-proof their organisation. In telecommunications, one important concept to understand is SIP Trunking.

Telecoms is an industry not short on acronyms. Alongside VoIP, IP PBX, ISDN, PSTN and more, SIP – and specifically SIP Trunking – are becoming increasingly important. For the uninitiated, they are well worth getting your head around.

Keeping tabs on the various different terms and new tech can be a challenge, so we’ve rounded up the most important elements of SIP Trunking in a handy guide to what it all means, and gone into a little more detail about how it can help your business.

What is SIP Trunking?

SIP stands for Session Initiation Protocol, and is essentially a way to make and end connections for data and voice transfers over the internet. The ‘trunking’ element is a bit of a red herring, as a trunk used to refer to a bundle of phone lines shared between users. Modern trunking refers to a virtual link between your PBX and the standard phone network (the PSTN), using an internet connection.

Any business with a modern IP PBX (a PBX that supports the use of SIP to transfer data) also needs a way to connect their exchange to the wider PSTN. Traditionally (with older PBXs) this was done using ISDN. Now, with ISDN slowly being phased out, SIP Trunks are becoming the industry standard for connecting business phone networks over the internet.

Why are businesses using SIP Trunks?

Cost savings

WIth ISDN, businesses often end up paying for capacity they never use. SIP Trunks are packaged far more accurately around your business’s actual usage. And, more importantly, once you’re set up with a SIP Trunk provider, line rental and calls are usually significantly cheaper.

Geographic flexibility

SIP Trunks remove the location-based restrictions on telecommunications, meaning you can choose any number, regardless of geography. Perfect for international-based customers or suppliers. You can move office – even move country – and keep the same number.


Trunks are easy to scale up or down, depending on usage. For example, if your organisation suddenly experiences significant growth, don’t worry about physically installing new ISDN lines. Upgrading your number and capacity of trunks is simple and easy.

Unified Communications

From calls and texts, to emails, instant messaging and conferencing, SIP Trunks are the crucial building block in linking an organisation’s multiple methods of communications into one unified solution.

How easy is it to get started?

As trunking is a virtual, rather than physical installation, businesses should expect trunks to be set up and working quickly – even within 48 hours. In most cases organisations can just use their existing internet connectivity and infrastructure, with no need for extra installation.

SIP Trunk providers with significant experience and expertise can help get you the right combination of services quickly and easily.

As you would expect, fast, reliable internet connections are crucial, as is having a modern IP PBX and IP enabled phones.

Want to know more?

Gradwell were one of the UK’s SIP Trunk pioneers, developing the technology when it was still relatively nascent. Our services are now trusted by thousands of SMEs and larger businesses around the UK. Take a look at our SIP Trunk services to see how we can help you.

Get in touch with an expert today.

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