If you have spent any time looking at telecoms options in the recent past, then you will almost certainly have come across the concept of SIP trunking. What SIP trunking does is to replace the old ISDN line you used to need to connect your PABX to the telephone network. Instead it connects to the PSTN via the internet.

There’s a little more to SIP trunking than that, however, so here are some key things you need to know.

VoIP wholesale carrier adoption

More companies are turning to VoIP based communication form established specialists such as IDT. This, in turn, means that more of them are adopting the use of SIP trunking. This covers businesses of all sizes, not just large enterprises but smaller companies too.

Part of the reason for this popularity is that using SIP trunking can deliver significant savings. This is partly because the cost of renting an internet connection is much less than that of an ISDN line. Plus, of course, call costs are cheaper on VoIP, in some cases you may get free local landline calls, and calls to mobile and international numbers will be significantly cheaper.

Communication strategy

Many businesses are seizing the opportunities offered by switching to VoIP to revamp their entire communication strategy. Installing SIP trunking can help in enabling a Unified Communications (UC) strategy. It means that your phone system can talk to the public network, but allows mobile apps and computer-based conferencing and video calling systems to connect too. SIP trunking also helps if you are considering moving to a cloud-based PABX system, which is often something businesses consider as part of a UC strategy.

You do need to ensure that your SIP trunking is going to be compatible with any existing system you intend to keep, even if only in the short term. Many businesses will have invested in expensive PABX systems and won’t want to write that off. It’s important to check with your SIP trunking provider that it’s going to be compatible. Most will offer interoperability checking to ensure that everything is going to work.

If your business operates across multiple sites, you may well have PABXs at each of them connected by ISDN circuits. SIP trunking allows you to rationalise this with fewer expensive connections needed and a single cloud PABX to serve the entire business. This can not only streamline the operation but also deliver substantial cost savings.


One of the major advantages of SIP trunking is that it can readily adapt to your business requirements. It’s easier to scale up as you expand and also to adapt to varying seasonal requirements. It’s simple to add extra trunks if your need to increase call volumes. Some businesses have particular seasonal peaks in demand when they need to make and receive extra calls. SIP trunking allows you to accommodate this without having to pay for infrastructure that lies underutilised for much of the rest of the year.

There are advantages too if you need to move premises but keep your existing numbers. It allows you to vary your outbound numbers so, for example, your calls can appear to be local to your customers even though they are actually being made from a call centre elsewhere.

Security and resilience

Switching to any internet-based service inevitably raises concerns over security. This is understandable, but as with any system, the key to security lies in its correct implementation. If you take appropriate measures then a SIP trunked system should be no less secure than a conventional telephone system. It also gives you more control because you can manage your own connection and the firewalls and routers associated with it, giving you the opportunity to put in place security measures to suit your operation.

If you rely heavily upon voice communication then, of course, you need a reliable system. Whatever type of system you have this means having a robust disaster recovery plan in place. SIP can actively assist your disaster planning as it makes it much easier to divert resources to another site in the event of a problem. What’s more, you can do so with no concerns about geographical location and without incurring costs for call forwarding. Traditional phone systems might mean a wait of 24 hours or more before call forwarding kicks in, with SIP trunking it can be virtually instant.


SIP trunking is all about enabling connectivity. It offers enterprises enormous flexibility in addition to substantial potential savings. To make the most of this, you need to understand your business’ communication requirements. That means analysing call volumes and working with your service provider to ensure you have the bandwidth needed to cope. Whether it’s just for voice or as part of a UC strategy SIP trunking has many positive benefits.