PSTN vs VoIP: What’s changed and what’s changing in 2025

The Public Switched Telephone Network (PSTN) is the legacy telephony network that connects calls via physical phone lines. The PSTN is scheduled to be phased out in most countries by 2030, meaning traditional landline phones will go out of service:

Voice over Internet Protocol (VoIP) is the internet-based telephony system that is replacing PSTN. VoIP transmits calls over the internet, and it’s easy to scale and customize. VoIP has been around for years and is finally set to replace the PSTN.

As mobile network operators transition their infrastructure to run completely on VoIP, the PSTN will remain in effect. This article explains how the PSTN works, its benefits and disadvantages, and how VoIP will replace its functionality. As the PSTN is being phased out at both national and international levels, businesses that still rely on the traditional network must begin preparing for the transition as soon as possible.

Telnyx has the infrastructure and technical expertise to help businesses migrate to a scalable VoIP network that preserves the security and functionality of the PSTN, with added benefits such as lower costs and state-of-the-art digital integrations. Before we get into that, let’s look at what the PSTN is, how it works, and how it contrasts with VoIP.

What is the PSTN?

The PSTN is a collection of interconnected public telephone networks that rely on physical infrastructure, such as copper wires and telephone lines, to connect callers. It’s the traditional “landline” phone network that uses circuit switching to connect calls via telephone poles and lines across the world.

The PSTN is also known as the Plain Old Telephone Service (POTS), because it’s well-established and straightforward. It doesn’t rely on an internet connection, and it continues to work during power and internet outages. On the other hand, the plain old service comes with plain old functionality: all you can do with it is make and receive voice calls. The PSTN does not support features like conference calling, call recording, or intelligent call routing.

The telecommunications industry is seeing a decline in demand for PSTN lines, particularly in areas where PSTN replacement is imminent. The PSTN is a global network of physical infrastructure, so the transition away from the PSTN to a predominantly digital telephony system is a massive undertaking.

Although the PSTN still uses telephone lines and copper wires, over the years it has shifted to take advantage of some new technologies. It no longer relies on human telephone operators to connect calls, and can connect to digital desk phones. Still, these upgrades are no match for the demands of today’s callers.

How the PSTN works

When you pick up the phone and dial, several things take place that enable your call to connect:

1. Dial tone and number entry The caller picks up the phone, hears a dial tone, and dials a number.
2. Voice signal conversion The phone converts sound waves into electrical signals.
3. Signal transmission to terminal Those signals travel via cables to a terminal.
4. Routing at the central office The terminal sends the signals to a local exchange (central office), which determines how to route the call.
5. Long-distance transmission The signals travel through the network—via copper wires or fiber optics—as electrical or light pulses, depending on the cable type.
6. Destination delivery Once the call reaches the recipient's local exchange, it's routed to the correct terminal.
7. Sound conversion on the other end The recipient’s phone converts the electrical signals back into sound waves, enabling real-time communication.

PSTN infrastructure

When you place a call on the PSTN, it passes through multiple touchpoints, or offices, before reaching the phone on the other end of the line. The call travels through physical wires to each relevant office until it reaches its intended receiver. Here’s a breakdown of the key touchpoints:

• Central office (local exchange):
  Connects individual subscribers to the PSTN based on geography. It identifies the dialed number and sends the call to the next network layer.
• Tandem office:
  Acts as an intermediary between local exchanges. It handles call routing across broader geographic regions.
• Toll office:
  Manages long-distance domestic calls. For example, it routes a call from California to New York if the destination is outside the local or tandem office’s coverage.
• International gateway:
  Handles switching for international calls. When dialing a number outside your country, this gateway ensures the call reaches the correct international network.

Pros of the PSTN

The PSTN’s main benefit is that because it operates independently from local power or IP network infrastructure, it’s consistent. Barring telephone line damage, it will continue to function through power outages or poor internet connectivity. Its independence means it’s currently more reliable and secure than digital alternatives.

Reliability

The PSTN’s independence from power sources and internet connectivity makes it ideal for emergency services, such as:

• 911 calls
• Fire alarms triggering an alert to the local fire department
• Medical alert services
• Security systems communicating location information when an alarm is triggered

Further, because of the way calls are routed through the PSTN, it’s possible to physically trace the origin of any call. This makes it ideal for emergency services; even if a caller is not able to identify or communicate their location, the 911 dispatcher can trace the call and send help to the correct place.

Security

The Center for Strategic and International Studies estimates that cyber attacks cost businesses over $600 billion dollars worldwide each year. IP-based communications like VoIP have security vulnerabilities that make them susceptible to some forms of cyber attacks. The software, data networks and wireless data transmission that are often involved with VoIP communications present potential access points for security breaches.

The PSTN, on the other hand, is still mostly built on copper wiring. To compromise the security of PSTN voice communications, one would have to physically access the phone lines by “bugging” or “wiretapping:” two (illegal, except in specific instances) methods of listening in on phone calls.

Transitional flexibility

Migrating to internet-based technology, such as VoIP, is done on a per-line basis in a deliberate and methodical process. IP-capable infrastructure still needs to be built out to some rural areas, so carriers must make physical improvements before completing the switch. In the meantime, the PSTN remains in place as a failsafe until VoIP and wireless solutions are deemed stable and secure enough to be used for all global voice communications.

Cons of the PSTN

The main downside is that the amount of infrastructure and touchpoints involved makes it challenging to match the instant data transmission offered by modern telephony solutions, such as VoIP.

Features

PSTN users are limited to voice data and a few basic features like Caller ID and voicemail. That is an inadequate suite of options for contemporary businesses that expect intelligent call routing, multiphone conferencing, and transcription/translation.

Cost

The PSTN costs users far more than digital alternatives. An on-premise landline can cost businesses as much as $20,000. Coupled with payment plans based on users rather than minutes, landlines can cost businesses 50% more than VoIP.

Scalability

On-premise phone networks built on the PSTN lock employees into coming into the office to conduct company business. This method of doing business is more secure, but it limits mobility and the ability of businesses to scale operations to an enterprise level.

Let’s dive further into how VoIP compares to the PSTN and how providers like Telnyx can help businesses take advantage of VoIP’s functionality while maintaining a secure infrastructure.

PSTN vs. VoIP

PSTN requires both local and global physical infrastructure to function, fundamentally in the form of copper wires. VoIP is packet-switched and uses internet networks that are shared with other internet-based services.

With VoIP, you can create calling systems as simple or complex as your needs require, equipped with automations, conferencing capabilities, advanced privacy and security configurations, call recording, translation, transcription, and integrations with other communication channels, such as messaging or video—all on a network built to scale.

If you’re still not sure which telephony solution is right for your needs, read our in-depth guide that is designed to help you decide.

In a head-to-head comparison, security is the only area where the PSTN comes out ahead. However, VoIP providers like Telnyx, who operate on proprietary IP networks, are able to meet rigorous security standards by keeping call data off the public internet entirely, while providing advanced networking configuration options, including VPN solutions.

The global PSTN decommission timetable

Given that PSTN is both expensive and limits scalability compared to internet-based systems, it’s no wonder that most industrialized countries have scheduled VoIP to replace the PSTN in the near future. While there’s no comprehensive decommission timetable, many of the world’s major economic powers have already phased out the PSTN or are actively in the process of doing so.

The Netherlands was way ahead of the curve: the country’s main telecommunication provider shut down their PSTN and switched to VoIP back in 2018. Australia is in the process of switching off its PSTN as part of its National Broadband Network rollout. The U.K. has announced that it will phase out PSTN by 2027. Germany switched off their PSTN in 2018, catching many businesses off guard and leading to confusion over the timetable for making the transition to VoIP.

Transitioning from PSTN to VoIP with Telnyx

In order to ensure you choose the right VoIP provider, it’s important to remember the qualities the PSTN possesses that have served us so well over the past decades, and seek their equivalents when selecting a compliant PSTN replacement service. This way, your calling system can function appropriately in an emergency and meet regulatory compliance standards.

Selecting a VoIP provider that operates on a proprietary IP backbone can help reduce vulnerabilities to cybersecurity attacks. Telnyx VoIP processes calls on a private, global, carrier-grade network that is isolated from the public internet. It also offers networking solutions that enable businesses to apply advanced security measures to their internet-based communications.

Telnyx for PSTN replacement service enables fast, reliable number porting services that keep phone numbers intact while transferring them quickly from landline to virtual. Ensuring that porting goes smoothly minimizes the inconveniences of transitioning your phone system from landline to digital.

SIP trunking: the bridge from PSTN to VoIP

Session initiation protocol (SIP) is the technology that allows businesses to bridge legacy PSTN systems to modern VoIP platforms. SIP enables voice and video calls over the internet through a text-based protocol similar to HTTP.

Because SIP allows for interoperability between different types of networks and devices, VoIP services use SIP as both the primary signaling protocol and as a tool to convert analog voice signals into digital signals that can be transmitted over the internet.

Telnyx SIP Trunking allows users to take advantage of advanced capabilities like automated number porting, integration with video conferencing platforms, and custom call routing. Telnyx SIP Trunking also allows for emergency calling features and secure connectivity thanks to Telnyx’s private, multi-cloud network.

Programmable, scalable, secure

Telnyx VoIP platform combines what’s great about the PSTN with advanced features that modern businesses expect:

Programmable Gain full control over your communications with custom setup, robust API and SDK integrations, and detailed debugging tools in the Mission Control Portal.

Scalable Our global network delivers high-quality voice calling in over 140 countries with minimal latency. Telnyx customers save up to 30% compared to other providers thanks to pay-as-you-go billing and automatic volume discounts.

Secure and compliant Inbound call screening protects your voice channels by blocking unwanted traffic, while our global operating licenses help ensure compliance with local telecom regulations.

The PSTN still offers a degree of reliability, but its global replacement by VoIP is well underway—and gaining momentum.

Regardless of where businesses operate in the world, the PSTN will remain viable for only a few more years. VoIP, on the other hand, will continue to evolve as long as the internet is used. The sooner businesses begin the transition, the better.