PSTN and ISDN Switch-Off 2025: What Businesses Need to Know & Why Move to VoIP

Introduction

In December 2025, a seismic shift will occur in the world of business communications—the complete switch-off of the Public Switched Telephone Network (PSTN) and the Integrated Services Digital Network (ISDN). This isn’t merely a technical upgrade; it is a fundamental digital migration that will affect millions of organizations across the UK and beyond, forcing businesses to reimagine how they connect, operate, and serve customers.

If your business still relies on traditional phone lines, alarms, EPOS systems, fax machines, or any device operating through PSTN or ISDN lines, immediate action is essential. With the sunset of these legacy networks, traditional landlines will go silent, and systems depending on dated copper infrastructure will cease to operate. The only way forward is embracing a modern alternative: Voice over Internet Protocol (VoIP).

This sweeping change brings challenges and opportunities. Businesses slow to adapt face possible disruptions, downtime, loss of revenue, and compromised customer service. Those that act swiftly, however, can reap the benefits of more flexible, scalable, and cost-effective communications. This blog unpacks what the PSTN/ISDN switch-off means, which systems and sectors are at risk, why VoIP is the ideal solution, and how your business can prepare smoothly for the transition.

What Are PSTN and ISDN—and Why Were They Dominant?

Before diving into the switch-off, it’s important to understand what PSTN and ISDN are and why these technologies have underpinned business communications for decades.

PSTN is the historic copper-wire network used for nearly every landline call made over the last century. It is entirely analog, designed in an era when phone calls and simple data transmission were the lifeblood of communication.

ISDN, developed later, is a digital technology that leverages the same copper lines but allows for transmission of both voice and data over the same connection—with higher quality and additional functions such as video conferencing and multi-line calls. ISDN represented a leap forward for organizations needing richer, business-grade communications, particularly before dedicated internet connections became widespread.

For decades, PSTN and ISDN powered not only voice calls but also alarm bells, payment terminals, fax machines, lift telephones, and even certain types of broadband reliant on copper lines. Their simplicity and reliability made them universally adopted in business.

Why Are PSTN and ISDN Being Switched Off?

You might wonder why these “tried and tested” networks need replacement at all. The reasons are compelling and inevitable:

Aging Infrastructure: The copper cables buried under streets have reached the end of their life, are becoming unreliable, and are expensive to maintain.
Changing Demands: Modern businesses require much more bandwidth, speed, and flexibility than copper lines can support.
Cost and Resources: Maintaining two parallel infrastructures—analog and digital—makes little economic sense.
Technology Progress: The world is moving to all-digital, all-IP communications. Cloud telephony, fibre broadband, and VoIP offer vastly superior features at a fraction of the cost and complexity.

The switch-off means telcos, like BT/Openreach, can invest in modern fibre infrastructure, delivering faster and more reliable digital services to businesses and homes.

The Switch-Off Timeline: Key Milestones

The phase-out of PSTN and ISDN has been underway for years. Here are the key milestones vital for business planning:

2017–2020: Announcements and trial “stop sell” phases begin in select regions. No new PSTN/ISDN lines are available in pilot areas.
2021–2023: Nationwide expansion of stop-sell—businesses in many locations can no longer order or change PSTN/ISDN services.
December 2025: Full PSTN and ISDN switch-off. All remaining lines will be permanently decommissioned. Any devices dependent on these networks will stop working.

If your organization is even partially reliant on PSTN or ISDN, immediate audit and migration planning is urgent to avoid last-minute panic.

Which Systems Will Be Affected?

The impact of the switch-off goes far beyond traditional phone handsets. Any system or device plugged into a legacy phone socket is at risk—including many that businesses may overlook:

Desk and conference phones (using analog or ISDN lines)
Broadband connections (like ADSL, FTTC) using copper infrastructure
EPOS (Point of Sale) machines
Alarm systems—fire, intruder, and telecare systems
Fax machines
CCTV and security monitoring systems
Door entry/intercom systems
Lift telephones
Payment terminals and card readers
Emergency lines

Businesses in every sector—retail, hospitality, manufacturing, healthcare, real estate, government—depend on a complex web of legacy systems, often with little visibility over precisely what connects where. The risk is not just inconvenience but outright business disruption if overlooked.

The Scope of the Business Risk

Millions of businesses in the UK alone, and many more globally, still use at least some element of PSTN or ISDN infrastructure. Small businesses, particularly with single sites, often don’t realize the full extent of their exposure. Large organizations face complicated migrations across multiple locations, sometimes with legacy systems integral to safety or compliance.

Primary risks of inaction include:

Loss of all voice and data services: When the switch-off happens, analog lines go dead—no dial tone, no call forwarding, no voicemails, nothing.
Security breaches: Alarm lines, lift phones, and emergency connections will not function, exposing businesses to breaches and liability.
Payment and operations failure: Card terminals and EPOS systems dependent on legacy lines will be non-functional, disrupting commerce.
Reputational damage: Customers expect fast responses. A business that “goes dark” or fails basic communications expectations will lose trust.

For multisite and regulated businesses—like healthcare and banking—the stakes are even higher.

Why Move to VoIP?

With PSTN and ISDN disappearing, the recommended (and often required) solution is VoIP: Voice over Internet Protocol. Here’s why it’s the clear winner.

What Is VoIP?

VoIP transmits voice and multimedia communications via the internet rather than copper wires. All that’s needed is a broadband connection and VoIP-compatible hardware or software.

Benefits of VoIP for Businesses

Business Continuity: Call forwarding, virtual receptionists, and disaster recovery features keep your communications live, everywhere.
Productivity Boost: Advanced features (call recording, auto-attendant, voicemail-to-email, UC integration) streamline workflows and support hybrid or remote teams.
Scalability: Add or remove users or locations in minutes—not weeks. Perfect for growing businesses.
Cost Savings: No need to maintain expensive copper lines; many VoIP providers offer all-inclusive pricing.
Flexibility: Employees can work from any location using the same number on desk phones, mobiles, or computers.
Reliability and Security: Modern VoIP is protected with encryption and redundancy—far more robust than aging analog setups.
Integration: Seamless compatibility with CRMs, collaboration tools, and other cloud-based business apps.

Are There Alternatives to VoIP?

While some companies use SIP trunking (digital voice over IP pipes) as an intermediate step, VoIP and hosted cloud phone systems are widely considered the end-state for organization-wide transformation. SIP trunks may allow keeping legacy on-premise systems, but real savings and features typically come with a full cloud migration.

How to Prepare: Step-by-Step Business Guide to VoIP Migration

A successful migration requires planning and action well before December 2025. Here is a best-practice migration framework:

1. Audit Your Infrastructure

Draw up a complete inventory: phones, broadband lines, alarms, payment and EPOS systems, fax, lift lines, intercoms.
Document connection types—identify anything still plugged into analog sockets or using ISDN services.
Assess broadband capabilities; VoIP needs robust, reliable internet.

2. Evaluate VoIP Providers and Solutions

Shortlist VoIP providers with proven experience in your sector.
Consider cloud-hosted PBX, SIP trunking for legacy systems, or hybrid solutions for phased migration.
Ensure your provider offers migration support for all special services (alarms, EPOS, CCTV, etc.).

3. Prepare Your Internet Connection

Install or upgrade to full fibre (FTTP) if available—essential for high-capacity, reliable office VoIP.
Consider backup connections (4G/5G failover or secondary fibre) for critical sites.

4. Update Hardware and Train Staff

Replace or adapt devices that can’t connect to VoIP—many systems offer adapters for old handsets, but often it’s easier (and cheaper long-term) to upgrade.
Provide user-friendly guides and training—VoIP offers much more, including mobile apps and seamless work-from-anywhere functions.

5. Pilot and Test

Run a short pilot test for key departments or branches. Proactively identify and resolve teething issues.
Test all critical systems—especially emergency and compliance-driven lines.

6. Full Go-Live and Support

Launch to all sites and all users, monitoring quality and user experience.
Set up ongoing support with your VoIP provider—all reputable partners offer 24/7 monitoring and rapid response teams.
Keep a fallback plan for unforeseen issues.

7. Decommission Legacy Systems

Once VoIP is proven and stable, arrange for secure, environmentally responsible disposal of redundant analog and ISDN equipment.

Common Questions and Challenges—Answered

Q: Will my alarm system or lift phone be affected by the switch-off?
Absolutely. Any device using a legacy phone socket or ISDN line will lose connectivity. Review all such lines, especially in older or multi-use buildings.

Q: Is internet telephony (VoIP) as reliable as my old landline?
Yes, provided you have business-grade broadband and a reputable provider. Built-in redundancy, call failover, and automatic rerouting make VoIP extremely robust.

Q: What if my broadband isn’t fast enough for VoIP?
Most business-grade lines are more than sufficient. Generally, a single VoIP call needs only 100 Kbps up/down. For multiple concurrent calls, upgrading to full fibre is wise.

Q: Will VoIP be more expensive?
In almost every case, businesses save money—no line rental, reduced support costs, and consolidated billing. Feature-rich packages mean less reliance on third parties for add-ons and integration.

Q: Can I keep my existing phone numbers?
Porting is standard practice—reputable VoIP providers handle this for you with no loss of service.

Q: Do I need new handsets?
Not always, but many businesses take the opportunity to upgrade to VoIP-enabled devices for better features and call clarity.

Q: What is SIP trunking and is it right for my business?
SIP trunking replaces ISDN but still requires enough on-site infrastructure. It’s sometimes suitable for larger organizations wanting to retain investments in existing phone systems before moving fully to the cloud.

Don’t Wait—The Risks of Delaying Migration

As December 2025 nears, demand for VoIP installations, audits, and technical expertise is soaring. Suppliers and engineers are booking out months in advance. Delayed action could result in:

Missed installation slots and protracted downtimes.
Business disruption as critical lines “go dark.”
Inability to process payments, answer customer inquiries, or ensure safety compliance—resulting in lost revenue and reputational harm.

Businesses that migrate early report easier transitions, more choice, and lower stress.

Action Plan: Get Ready for a Smooth Switch

1. Act Now:
The worst mistake is waiting until the last minute.

2. Book a Communications Audit:
Many VoIP providers offer free reviews of your current setup and objective advice.

3. Involve the Right People:
IT, facilities, security, and finance all need representation to ensure no overlooked systems.

4. Shortlist Providers and Get Quotes:
Prioritize companies with proven migration experience and all-in support.

5. Train Your Teams:
Smooth the transition by helping staff get familiar with new communications tools and dashboards.

6. Set a Go-Live Date and Decommission Old Lines:
Coordinate with your provider for a seamless switchover, keeping fallback options in place.

Conclusion

The PSTN and ISDN switch-off signals the end of an era in business communications. This is not just a technical event—it’s a once-in-a-generation opportunity to propel your business into the digital-first world, leveraging modern, flexible VoIP solutions for all your operational needs. Those who act now will secure greater efficiency, security, employee satisfaction, and future readiness. Don’t let your business “go dark”—embrace the change and move confidently forward with VoIP. The time to prepare is now.