Buy the channels you need
Size around peak concurrent calls and sensible headroom rather than paying for one line per user.
SIP trunking / UK
Keep the PBX. Replace the old lines.
Use SIP trunks to connect a compatible phone system to the public telephone network over IP, with the capacity, number porting and failover planned properly.
Keep existing numbersClear migration planUK support
What this can include
SIP trunking with the failure modes designed out.
The trunk itself is only one part of the service. Capacity, routing, number presentation, firewall behaviour, carrier failover and migration all need to work together.
Port and present numbers correctly
Plan inbound ranges, outbound CLI and porting before cutover.
Build alternate routes
Use secondary destinations or resilient network design so a single failure does not mean silence.
Validate the PBX first
Check vendor support, codecs, authentication and firewall behaviour before assuming an existing platform is ready.
Designed around the workplace
Modernise the line while keeping the PBX that still works.
SIP trunking is often the right route when an existing PBX is still useful. Capacity, number ranges, routing and failover need to be designed around real concurrent-call demand and business continuity.
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How we deliver it
A cleaner route off ISDN.
01
Audit PBX and numbers
Confirm platform compatibility, DDI ranges, channels and dependencies.
02
Model concurrency
Use busy-hour demand and growth headroom to size channels.
03
Configure and test
Set authentication, routes, codecs, presentation and failover.
04
Port in a controlled window
Move numbers with agreed testing and support during cutover.
Is it right for you?
Where this option works best.
SIP trunking is often the best answer when the existing PBX still has useful life and the main problem is legacy line connectivity.
Choose this when
You have a compatible PBX or UC platform you want to retain and need to replace ISDN/PSTN voice connectivity with IP-based trunks.
Consider another route when
If the PBX itself is unsupported, difficult to manage or unsuitable for hybrid users, a hosted or cloud phone system may remove more complexity than simply changing the lines.
We can help you choose.
Tell us what you have today and what needs to improve. We’ll explain the options and recommend the setup that best fits your business.
Plan the change carefully.
We plan number porting, call flows, connectivity and user training before the system goes live.
Tell us about your setup
Tell us what the system has to do.
We’ll use the information to size the setup and make the first conversation useful.
Useful next steps
Read more before you decide.
Use these guides to understand migration, system options and capacity before you get in touch.
Compare
Migration
Capacity
Phone-system architectures
Cloud, appliance/software and Yeastar + Teams integration compared by operating model.
Number porting timeline
See the main stages involved in moving business numbers to a new provider.
SIP channel calculator
Estimate a sensible starting point from concurrent-call demand rather than user count alone.
Common questions
Frequently asked questions.
Short answers to the questions we are most often asked about this type of system.
What is a SIP trunk?
A SIP trunk is an IP-based connection between a compatible PBX or communications platform and a telephony carrier, replacing traditional voice circuits for inbound and outbound calling.
How many SIP channels do we need?
Channels are based on simultaneous calls, not total users. Busy-hour concurrency, queued calls, transfers and growth should be considered before setting capacity.
Can SIP trunks keep our existing numbers?
Usually, yes. Existing numbers can often be ported to the new service, subject to carrier and number-range checks.
Do SIP trunks replace the PBX?
No. SIP trunks provide telephony connectivity to a compatible PBX or UC platform. If you want to remove the PBX itself, compare hosted VoIP or cloud PBX options.