What is SIP trunking and why are so many UK businesses talking about it right now?
Let’s tackle this together. If you have heard the term in meetings and nodded along while thinking you will search it later, you are not alone. Don’t worry, we have all been there.
Here’s the thing. SIP trunking is simply a way to make phone calls over the internet instead of old copper phone lines. With the UK PSTN switch off happening by January 2027, this is no longer a nice extra. It is becoming essential. No business wants silent phones because they left it too late.
At Cleartwo, we help businesses move from legacy lines to modern VoIP phone systems without stress. We manage the setup, number porting and support. You get 99.99% uptime and proper UK based help when you need it. Real people. Real support.
SIP Trunking UK Explained In Plain English
So what does SIP mean? It stands for Session Initiation Protocol. Sounds technical, but it is not scary. It simply sets up and manages calls over the internet.
SIP trunking connects your business phone system, usually an IP PBX or cloud PBX, to the wider phone network. Instead of physical lines, you use virtual ones. These are called SIP channels.
If you already know what VoIP is and how it works, you are halfway there. SIP trunking is the link between your internal system and external numbers. That is it.
Why SIP Trunking Matters Before The PSTN Switch Off
Let’s be honest. The main reason SIP trunking is growing in the UK is the PSTN switch off. By January 2027, analogue and ISDN lines will be retired. That is confirmed.
If your business still relies on ISDN, you will need another solution. SIP trunking supports the move from ISDN to IP. It keeps your numbers, improves flexibility and often lowers costs.
We explain this further in our guide to the ISDN switch off 2027. Between you and me, leaving it too late can mean rushed decisions and limited install slots.
How SIP Trunking Works With Your Phone System
Let’s make this simple. When someone calls your business number, the call travels over the internet instead of traditional PSTN lines. It passes through your SIP trunk provider and reaches your IP PBX or hosted VoIP system.
Your cloud PBX then decides what happens next. It can send the call to reception, route it to a queue, forward it to a mobile app or record it for compliance. This all happens in seconds.
If you are comparing setups like hosted PBX vs cloud VoIP, SIP trunking works with both. It gives you flexibility without tying you to old ISDN lines.
Main Benefits Of SIP Trunking For UK SMEs
Now for the part that really matters. Why choose SIP trunking?
- Lower call costs
- Scalable call channels
- Support for remote working
- Microsoft Teams integration
- Business continuity backup
- Simple number porting
- Flexible call routing
Cost savings often grab attention. Many SMEs reduce line rental and call charges by a large margin. But the real benefit is flexibility.
If you need more concurrent calls during busy periods, you can add SIP channels. If you downsize, you can reduce them. No engineer visits. No long wait times.
For teams using Microsoft Teams phone integration, SIP trunking supports Direct Routing. This allows you to make and receive external calls inside Teams without relying on expensive calling plans.
SIP Trunking And CRM Integration
Your phone system should do more than provide a dial tone. It should give you context.
With the right setup, SIP trunking works with your CRM. When a customer calls, their record appears on screen. Calls can log automatically. Notes are saved in one place.
This keeps your team organised and saves time. No more sticky notes or lost details.
For regulated sectors, call recording can support GDPR and MiFID II requirements. A managed provider like Cleartwo ensures your setup meets UK standards.
SIP Trunking Vs Hosted VoIP What Is The Difference
Don’t worry. This confuses many people.
Hosted VoIP is your full cloud phone system. It includes features like auto attendants, call queues, voicemail to email and reporting. SIP trunking is the connection that links your system to the outside world.
If you are starting from scratch, a complete VoIP phone system for UK businesses is often the simplest route. If you already have an IP PBX on site, SIP trunking can modernise it without replacing everything.
No judgement either way. It depends on your setup, plans and budget.
Why We Recommend CallSwitch One For SIP Trunking
Not all SIP trunk providers in the UK offer the same support. Some are fully self service. That can feel fine until something stops working.
At Cleartwo, we provide SIP trunking and hosted VoIP through CallSwitch One. We are official CallSwitch One resellers. You get a powerful UCaaS platform with hands on UK support from us.
This means competitive pricing, strong features and proper onboarding. Most importantly, you get ongoing support from a team that knows your business.
How SIP Trunking Fits Into Your Wider Digital Strategy
Your phone system should not sit alone. It connects with reporting tools, CRM platforms and security systems. Everything works together.
When your team logs in from home and calls route correctly, that is modern business telephony in action. No outdated lines holding you back.
If you are investing in digital tools or marketing, your communications should match that progress. SIP trunking helps align your front end and back end systems.
Frequently Asked Questions About SIP Trunking
What Is SIP Trunking And How Is It Different From VoIP
SIP trunking connects your phone system to the public phone network using the internet. VoIP is the wider term for making voice calls over the internet. VoIP is the method. SIP trunking is the connection to external callers.
Does The UK PSTN Switch Off Affect SIP Trunking
No. SIP trunking is part of the solution. As analogue and ISDN lines are retired by January 2027, SIP trunking allows businesses to continue making and receiving calls over IP networks.
Can SIP Trunking Work With Microsoft Teams
Yes. SIP trunking supports Teams Direct Routing. This allows external calls within Microsoft Teams and is often more flexible and cost effective.
How Many SIP Channels Does My Business Need
You need enough SIP channels to cover your maximum number of concurrent calls. If 10 people may be on calls at the same time, you need at least 10 channels. Cleartwo can review your usage and advise.
Is SIP Trunking Secure And Compliant In The UK
When configured correctly, SIP trunking supports encryption, secure authentication and compliant call recording. For businesses with GDPR or MiFID II requirements, a managed provider ensures your system meets UK standards.
If you are unsure whether SIP trunking is right for your business, no stress. Speak to Cleartwo and we will walk you through your options in plain English. You have got this.
