SIP Trunking
Not quite ready to move to cloud telephony?
With the public switched telephone network (PSTN) being switched off in 2025, you need to move away from your on-premises phone system if you haven’t already, including integrated services digital networks (ISDN).
Session initiation protocol (SIP) Trunking enables you to continue using your existing telephony equipment after the analogue switch-off. You can then choose when to move to cloud-based unified communications in the future.
It’s a reliable, secure and cost-effective way to manage voice calls using the data network that allows you to add external calling to your existing phone system and benefit from voice services over internet protocol (IP).
How does SIP Trunking work?
SIP Trunking connects your organisation’s existing on-premises phone system to our network using an IP connection, passing voice calls between your site(s) and the wider network.
We also give you access to a portal where you can configure call diverts and access detailed stats and usage reports for incoming and outgoing calls.
Why choose SIP Trunking?
Reduce cost and complexity
Connect to a single central site ─ no more paying for lines and ISDN channels you don’t need
Scale to your needs
Add or remove phone lines at short notice to cater for busier and quieter times
Use any IP network
Choose from our data connectivity options or use your own internet service
Increase visibility and control
Manage both inbound and outbound calls from our SIP Trunking portal
Flexible phone numbers
Keep existing phone numbers (even when moving location) and present different numbers for outbound calls
Smooth migration
Keep your existing phone system, with no need to install new cables or change numbers
You’re in control
Our secure SIP Trunking portal gives you the power to manage
your service with granular levels of control and visibility.
Customise your setup to suit your needs
Make changes to your settings in real time, for example call forwarding options
Access analytics to identify areas of improvement
FAQs
What’s a SIP channel?
What’s a SIP channel?
A SIP channel has the capability to support incoming and outgoing calls. Every SIP trunk contains a number of channels that act as virtual versions of telephone lines. The number of channels you need depends on how many calls your business makes at the same time.
What’s the difference between SIP and VoIP?
What’s the difference between SIP and VoIP?
Voice over internet protocol (VoIP) makes and receives phone calls over the internet or internal networks. SIP is an application layer protocol used to make and manage multimedia sessions including voice, video and messaging. SIP is mainly used to support IP technology such as VoIP calls.
What’s the difference between SIP and ISDN?
What’s the difference between SIP and ISDN?
SIP Trunking is a newer technology and allows voice and data to be carried on the same channel. It uses the internet or a private network to deliver voice and data through a single line, whereas ISDN uses the old network of copper cables to deliver voice and data.
What are the requirements for SIP Trunking?
What are the requirements for SIP Trunking?
To use SIP Trunking, you will need an internet or private connection, for example an internet protocol virtual private network (IPVPN), with good bandwidth and speed. You will also need a compatible session border controller (SBC) and private branch exchange (PBE).
Is there a limit on how many phone numbers I can have?
Is there a limit on how many phone numbers I can have?
You can have as many phone numbers from as many locations as you like.
What’s the difference between SIP Trunking and a hosted PBX?
What’s the difference between SIP Trunking and a hosted PBX?
IP Trunking creates a virtual link between your existing PBX and the PSTN using an internet-based or private connection. A hosted PBX brings you fully to the cloud and removes the need for on-premise infrastructure. This may be your preferred option if you are looking to replace your on-premise PBX.
Can Microsoft Teams integrate with SIP Trunking?
Can Microsoft Teams integrate with SIP Trunking?
Teams can integrate with SIP Trunking, providing businesses with additional features such as call recording, call routing and voicemail, while still using collaboration features. There are several ways to integrate SIP Trunking and we offer several specific solutions.
What you can expect from us
Expert
advice
Boost productivity, improve collaboration and get more from your investments
Commercial
flexibility
Transition to the cloud with ease, with tech and finance options that maximise return on investment
Sustainable
thinking
Support your ESG goals and reduce tech waste with our carbon calculator, mobile donation programme and recycling scheme
Security and
peace of mind
Stay secure and compliant no matter how, where or when your people work
Want to know how we can support you?
Choose your organisation type below
Discover our range of voice solutions
Discover our range of voice solutions
Get in touch with our expert team
Small & medium business
(11 - 249 employees)
Call 0800 298 8848
Large enterprise & Public sector
(250+ employees)
Call 0800 955 5590
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