Replace your ISDN lines before the 2027 switch-off — and save up to 50% in the process
If your business still relies on ISDN phone lines, the clock is ticking. BT is switching off the ISDN and PSTN network in January 2027, meaning every UK business will need to migrate to an alternative before that deadline — whether they’re ready or not.
SIP trunking is the natural replacement. It uses your existing broadband connection to carry voice calls, connecting your phone system to the public telephone network without the need for physical phone lines. You keep your existing numbers, keep your existing phone system in most cases, and gain significantly more flexibility and resilience than ISDN ever offered.
Microcare supplies SIP trunks through Voiceflex and Gamma — two of the UK’s leading SIP trunk providers — and manages the entire migration on your behalf. From number porting and system configuration through to ongoing support, we make switching straightforward.
Cut your phone costs significantly: Save up to 50% on line rental and up to 25% on call costs compared to ISDN. Inclusive UK call bundles mean predictable monthly bills with no surprise charges.
Keep your existing numbers: All your current phone numbers can be ported across to SIP — no need to change your business number, update your stationery or redirect customers. Even if you move offices, your numbers move with you.
Scale up or down instantly: Add or remove voice channels in minutes as your needs change — no engineers, no lead times, no long-term commitments. Ideal for businesses with seasonal peaks or rapid growth.
Built-in business continuity: If your internet connection or office becomes unavailable, calls can be automatically rerouted to mobiles, another site or a backup number — instantly and at no extra cost. No missed calls, no disruption.
Better call quality than ISDN: SIP trunking supports high-definition voice codecs, delivering clearer call quality than traditional ISDN lines — particularly on long-distance and international calls.
PSTN switch-off ready: SIP trunking is the direct, future-proof replacement for ISDN. Migrating now means you’re compliant before the 2027 deadline and can take advantage of cost savings in the meantime.
SIP Trunking Features
Number Porting
Transfer your existing geographic and non-geographic numbers (01, 02, 03, 08) to SIP with no interruption to service. We manage the porting process end to end — typically completed within 10 working days.
Number Flexibility
Choose phone numbers from any UK area code — ideal for businesses that want a local presence in multiple locations. Display different numbers on outbound calls depending on which team or department is calling.
Inbound Call Management
Take full control of how inbound calls are handled — set routing rules based on time of day, day of week, staff availability or caller location. Route calls to hunt groups, queues, voicemail or mobile devices from an easy-to-use web portal.
Call Recording
Record inbound and outbound calls for compliance, quality assurance and training purposes. Recordings are stored securely online with full search and retrieval tools. Supports MiFID II and PCI compliance requirements.
Auto Attendant / IVR
Present callers with a professional menu of options — "Press 1 for Sales, Press 2 for Support" — routing them to the right team automatically. Customise messages for opening hours, out-of-hours and bank holidays.
Fraud Protection
Both Voiceflex and Gamma include built-in fraud detection and spend limit controls as standard. Unusual call activity is flagged and blocked automatically, protecting your business from unexpected bills caused by phone hacking or misuse.
Disaster Recovery & Failover
If your primary site goes down, calls instantly fail over to a secondary location, mobile numbers or a cloud destination — with no manual intervention required. Business continuity is built in from day one.
Microsoft Teams Integration
SIP trunks can be connected to Microsoft Teams via Direct Routing, giving your Teams users full PSTN calling capability without a separate Microsoft Business Phone licence. Ideal for businesses already using Teams as their primary communication platform.
Why Choose Microcare for SIP Trunking?
Supplied through Voiceflex and Gamma
Microcare provides SIP trunking through two of the UK's most established and reliable providers — Voiceflex and Gamma, the UK's number one SIP trunk provider. Both networks carry millions of business calls daily, with 99.99% uptime guarantees and award-winning UK support behind them.
We manage the migration for you
Switching from ISDN to SIP doesn't have to be disruptive. Microcare plans and executes the entire migration — number porting, system configuration, testing and go-live — with minimal impact on your team. In most cases, your existing phone system can connect directly to SIP with no hardware replacement needed.
One provider for phones, broadband and IT
When your SIP trunks sit alongside your broadband connection and phone system — all managed by the same team — troubleshooting is faster, changes are simpler and nothing gets lost between suppliers. One bill, one point of contact.
Frequently Asked Questions
SIP (Session Initiation Protocol) trunking is a technology that uses your internet connection to carry voice calls, replacing traditional physical phone lines. Your existing phone system connects to a SIP trunk provider via your broadband or leased line, which then routes your calls across the public telephone network. It works alongside your current phone system in most cases — no replacement required.
BT is switching off the ISDN and PSTN network in January 2027. From that date, traditional phone lines will no longer work. Every UK business using ISDN needs to migrate to a digital alternative — SIP trunking, a cloud phone system or a hosted VoIP solution — before the deadline. Businesses that leave it late risk service disruption and emergency migration costs.
Yes. All your current geographic and non-geographic numbers can be ported to SIP trunking. The porting process typically takes up to 10 working days and Microcare manages it entirely on your behalf. Your numbers remain live throughout the transition with no interruption to service.
In most cases, yes. SIP trunking works with the majority of modern PBX systems. Microcare will assess your current phone system as part of the migration planning and advise on compatibility. Where a system upgrade is needed, we’ll recommend the most cost-effective path.
SIP trunking is typically charged per voice channel per month, with optional inclusive call bundles for UK landlines and mobiles. Costs vary depending on the number of channels you need and your call volume. Get in touch for a tailored quote — in most cases, businesses switching from ISDN see immediate savings of 30–50% on their line costs.
The number of SIP channels you need equals the maximum number of simultaneous calls your business makes or receives at any one time — not the number of users or extensions. Microcare can review your current usage to recommend the right number of channels, with the flexibility to scale up instantly if needed.
This is one of the biggest advantages of SIP trunking over ISDN. If your internet connection fails, calls can be automatically rerouted to mobile numbers, another site or a cloud destination — instantly and without any manual intervention. Microcare configures failover as standard so your business stays reachable whatever happens.
For most businesses, SIP trunking can be provisioned within a few days. Number porting typically adds up to 10 working days. Microcare manages the full process — from initial assessment through to go-live — and will agree a migration plan that minimises disruption to your team.
Yes. Both Voiceflex and Gamma include built-in fraud protection as standard, monitoring call patterns in real time and blocking unusual activity automatically. Spend limits can be set to prevent unexpected bills from misuse or hacking. For businesses with specific security requirements, SIP trunks can also be delivered over private access circuits rather than the public internet.
SIP trunking connects your existing on-premise phone system to the public telephone network via the internet — it replaces your phone lines, not your phone system. A cloud phone system replaces both the lines and the phone system entirely, moving everything to the cloud. SIP trunking is usually the right choice if you have a good existing phone system you want to keep. A cloud phone system makes more sense if you’re starting from scratch or want to move everything off-premise.
Enquire about SIP Trunking
Fill out this form and we’ll be in touch talk through SIP trunking.
Or call us right now on
0161 763 8801
"*" indicates required fields