Future-Proofing Business Connectivity Ahead of the PSTN Switch-Off 2027
With the UK’s PSTN and ISDN switch-off fast approaching (scheduled for January 2027), thousands of businesses are replacing outdated copper and ISDN services with fibre broadband and VoIP telephony.
This transition isn’t just about compliance — it’s a strategic opportunity to modernise your communications, improve performance, and reduce costs.
At Plum Communications, we specialise in guiding UK businesses through this journey. Here’s how we helped one client migrate smoothly from legacy fixed-line systems to a modern all-IP fibre and VoIP solution.
The Client: A well known Multi-Site North West UK based Firm
A regional firm with eight offices in North West England relied on ageing ISDN and ADSL infrastructure. Their challenges included:
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ISDN2/ISDN30 voice circuits nearing end of life
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Slow, unreliable ADSL broadband
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Multiple aged on-premises PBX
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High monthly line costs
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Poor integration between branch offices
With BT Openreach’s ISDN withdrawal underway, the firm needed a future-proof migration to fibre and VoIP — without service disruption.
The Challenge
Key objectives:
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Zero downtime during migration
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Unified fibre connectivity and VoIP telephony across all sites
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Hybrid work support for remote staff
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Lower telecom costs and simplified management
The Solution: Step-by-Step ISDN to VoIP Migration Plan
Plum Communications implemented a phased migration combining fibre Ethernet connectivity and cloud-hosted VoIP telephony.
Step 1: Connectivity Audit & Readiness Check
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Assessed fibre availability at each exchange
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Mapped existing circuits and network dependencies
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Upgraded LAN cabling to support PoE handsets
Step 2: Fibre Broadband & Leased Line Installation
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Deployed FTTP and Ethernet leased lines for high-speed, resilient connectivity
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Eliminated dependence on copper lines
Step 3: Cloud VoIP & SIP Deployment
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Migrated all ISDN lines to SIP trunks
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Rolled out hosted VoIP with softphones, mobile apps, and Teams integration
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Retained all DDI numbers via seamless porting
Step 4: Dual Running & Training
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Parallel operation for 14 days ensured no service interruption
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Comprehensive user training improved adoption and confidence
Step 5: Decommission Legacy Systems
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Retired PBX and ISDN lines after testing
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Monitored bandwidth and call quality for 30 days post-cutover
Results: Faster, Cheaper, and Future-Ready
| Metric | Before Migration | After Migration |
|---|---|---|
| Connectivity | ADSL / FTTC | Fibre Ethernet (1 Gbps) |
| Voice platform | On-site ISDN PBX | Cloud-hosted VoIP |
| Monthly telecom spend | ~£3,000 | ~£2,400 approx |
| Uptime | ~97.5% | 99.99% SLA |
| Remote access | Limited | Full softphone & Teams support |
Outcome:
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reduction in telecom costs
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Zero downtime during cutover
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Unified multi-site communication
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Stronger disaster recovery and business continuity
Business Lessons from the ISDN Switch-Off
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Plan early. Fibre installations can take months — don’t wait for the 2027 deadline.
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Audit your systems. Understand dependencies before disconnecting ISDN lines.
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Choose the right VoIP platform. Evaluate reliability, integrations, and SLA guarantees.
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Train your people. Staff confidence drives adoption and productivity.
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Partner with experts. The right telecom consultancy ensures a structured, low-risk migration.
Why Upgrade to Fibre and VoIP Now
Migrating from ISDN to VoIP is more than a compliance exercise. It brings tangible benefits:
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Higher call quality and HD voice
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Flexible hybrid work options
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Lower operating costs
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Scalable connectivity
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Improved resilience and security
And with Openreach’s stop-sell already in effect, delaying could limit your options for line rental and number portability.
About Plum Communications
Plum Communications helps UK organisations audit, design, and migrate their telecom infrastructure for the all-IP future.
Our services include:
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ISDN and PSTN migration planning
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Fibre and Ethernet connectivity solutions
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Hosted VoIP and SIP trunking
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SLA negotiation and contract management
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Business continuity and resilience design
Get Ready for the PSTN Switch-Off
If your organisation still depends on ISDN, PSTN, or copper lines, act now to avoid disruption.
Contact Plum Communications for a free connectivity audit and tailored migration roadmap.
Get ahead of the 2027 PSTN switch-off — modernise your business communications today.