The PSTN Switch Off
Is legacy telephony reaching its end? Around the world, carriers are phasing out the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) in favor of all-IP infrastructures. And this transition is critical for those operating a contact center, managing on-premises PBX systems, or building modern communications.
Many countries have already completed or nearly completed migration away from PSTN/ISDN. Others have published formal deadlines for shutting off copper infrastructure. Meanwhile, many countries are in phased migration mode, meaning new orders of legacy lines are restricted, carriers are pushing customers to move to IP, and copper maintenance is increasingly costly.
This post breaks down what’s happening, when these shutdowns are expected, why carriers are retiring these technologies, and how you can prepare for the future of cloud telecom.
What is PSTN?
The PSTN is the decades-old copper-based infrastructure that supports traditional analog landline calls. It uses circuit-switched technology: dedicated physical paths between endpoints.
What is ISDN?
The ISDN is a digital upgrade introduced in the 1980s that transmits voice and data over copper lines. It provided multiple channels, faster setup times, and early forms of digital communication.
Both systems rely on the same copper network. Both are now classified as legacy.
When is the PSTN switch off happening?
Answer: It depends on the country.
United Kingdom
The UK has the clearest timeline:
PSTN/ISDN stop-sell began in 2023.
No new copper-based services can be ordered.
The final shutdown target is for the end of January 2027.
United States: A gradual sunset by state
The U.S. has no single national shutdown date. Instead, it’s being rolled out on a state-by-state basis. But the decline is undeniable, as carriers have been retiring copper networks region by region. Analog and ISDN pricing has increased sharply while many local service areas have stopped offering new PSTN orders.
The shift is happening, just without a single, official cutoff date.
Europe and APAC: Varies by country
Several countries have already shut down legacy networks. Others have announced timelines or begun phased withdrawals. The global trend is consistent: copper is ending and IP is the future.
Why are PSTN and ISDN being retired?
Carriers worldwide are decommissioning these technologies. The drivers are consistent across markets:
1. Copper infrastructure is obsolete
The PSTN cannot support modern communications workloads, including high-bandwidth data, video, and cloud-native voice traffic. Maintenance is increasingly difficult due to aging equipment and shrinking expertise.
2. Rising cost and operational burden
Copper networks require specialized engineers, legacy hardware, and constant physical maintenance. Providers are aggressively reducing these costs by shifting to all-IP networks.
3. Strategic move to Voice Over Internet Protocol (VoIP)
VoIP is now the global standard. IP networks offer easier management, better scalability, rapid provisioning, and native compatibility with cloud applications and APIs.
How to navigate the PSTN switch off
When PSTN and ISDN disappear, any service still running on copper lines will stop working unless moved to an IP. That includes:
Legacy PBX systems
Fax machines tied to analog lines
Elevator phones and building entry systems
Alarm systems and emergency endpoints
Modems and telecare devices
If you’re not prepared, outages will be unavoidable.
The future of telecom is in the cloud, and this switch off is a turning point for communications strategy. It’s a great opportunity to:
Consolidate fragmented systems into a unified telecom architecture
Adopt programmable SIP or cloud voice platforms
Use APIs to modernize routing, call flows, and data integrations
Build or integrate real-time voice AI agents
Eliminate hardware dependence entirely
Modernizing telephony infrastructure
Migration to the cloud is an opportunity to evolve. Once copper services are retired or restricted, organizations must shift to IP-based communications. This can be a straightforward replacement (like SIP trunks for ISDN lines), or it can be a complete modernization of the voice architecture.
The right approach depends on availability, continuity requirements, regulatory needs, and the sophistication of your communications workflows. Here are the primary modernization paths:
SIP trunking and programmable SIP
A direct IP-based replacement for ISDN or analog lines.
Uses your existing broadband connection instead of copper circuits
Supports number porting, DID mapping, and enterprise call routing
Works with most on-premises PBXs and SBCs
Easier to scale than ISDN (no physical channels)
SIP trunking is the fastest path for organizations that want to keep legacy PBX systems but eliminate copper.
Hosted PBX/Cloud PBX
A cloud-delivered phone system that replaces your on-premises PBX hardware.
Reduces hardware, maintenance, and upgrade requirements
Provides VoIP endpoints, softphones, and web clients
Often includes voicemail, interactive voice response (IVR), auto-attendants, and call queues
Acts as a bridge between SIP and cloud workflows
Hosted PBX is popular for organizations wanting predictable costs with minimal infrastructure management.
WebRTC or browser-based endpoints
Modern, software-only endpoints for voice/video inside applications.
No hardware phones or SIP desk devices
Runs on mobile devices, browsers, or embedded apps
Perfect for omnichannel workflows, support portals, and agent desktops
Enables global connectivity without physical infrastructure
WebRTC complements SIP by providing a flexible edge that works anywhere an internet connection exists.
Legacy cloud communications platforms vs. Programmable Unified Communications (PUC)
Cloud communications platforms (also known as communications as a service: UCaaS, CCaaS, and CPaaS) provide complete voice infrastructure in the cloud. They can handle call routing, SIP endpoints, WebRTC, and voice recording.
They integrate with identity systems and enterprise apps, provide dashboards and programmatic APIs, and enable hybrid deployments.
This tier of communications offers more flexibility and scaling than traditional PBX models.
The newest category in this family, however, is Programmable Unified Communications (PUC). This option is preferred by developers who need to build differentiated customer experiences, automate routing, or integrate AI.
PUC represents the next evolution of business communications: a unified, low-latency infrastructure that is fully programmable at every layer, across voice, video, messaging, and AI.
It differs from UCaaS, CCaaS, and CPaaS in three key ways:
1. Unified infrastructure across all channels
PUC consolidates real-time voice, messaging, video, and AI onto a single programmable stack.
No more stitching together siloed products, PBX systems, and third-party APIs.
2. Programmability as a first-class feature
Instead of fixed features or vendor-defined workflows:
Developers can define routing, logic, and experiences
Every channel is API-driven and scriptable
Call flows integrate directly with LLMs, RAG pipelines, and data sources
Multi-agent voice or AI-driven interactions become native
This is essential as organizations move beyond simple VoIP into automated, intelligent communications.
3. Low-latency, cloud-native architecture
PUC platforms are built for:
Real-time voice media
Low latency voice, video, and AI communication
Programmatic routing
Live audio streaming
Multi-agent voice ecosystems
This architecture supports high concurrency, AI-first contact centers, and next-gen IVRs that can’t run on legacy UCaaS or PBX systems.
When to choose PUC
PUC is the right modernization path if you:
Need to integrate AI voice agents
Want cross-channel consistency for voice, video, messaging, and fax
Are replacing a complex stack
Require programmable, serverless, cloud-native communications
Need full end-to-end control over routing, experiences, and data
For developer-led companies or those building in-house communications products, PUC is the long-term replacement for legacy cloud communications services.
What comes after the PSTN switch off
The retirement of PSTN and ISDN sets the stage for the next era of telecom, one that SignalWire and FreeSWITCH have been ushering in for decades.
Communications become software-defined, the cloud and APIs replace hardware, and real-time communications become programmable. And in the new era of PUC, AI enters the network layer, while multi-modal communication becomes the default.
Ready to build the future of cloud communications? Try SignalWire today by creating a free account, and join our developer community on Discord.
FAQ
When will the PSTN be shut down?
The UK has a target date of January 2027. Other countries are sunsetting copper gradually but with no reversal in sight and no hard deadline.
Is ISDN being discontinued?
Yes. ISDN services are tied to the same copper infrastructure and are being phased out everywhere that PSTN is being retired.
Why is the PSTN being shut down?
Because copper networks are outdated, costly to maintain, and incompatible with modern IP-based communications.
What happens when PSTN lines are turned off?
Any device that relies on analog or ISDN lines will stop working, including PBXs, faxes, alarms, POS terminals, and elevator phones.
What replaces PSTN and ISDN?
VoIP, SIP trunks, fiber-based broadband, hosted PBX systems, cloud communications platforms, and voice APIs.
Is VoIP reliable enough to replace PSTN?
Yes. In many cases, VoIP exceeds PSTN reliability.
