PSTN replacement is the process of migrating voice infrastructure from the legacy circuit-switched public telephone network to IP-based connectivity, primarily through SIP trunking and DID numbers. It is not a future trend. It is an active, regulatory-driven transition happening on defined timelines across more than 30 countries simultaneously. For enterprises, operators, and service providers that still depend on physical copper lines or ISDN circuits, the window to migrate on their own terms is closing. C3ntro Global provides DID coverage for PSTN replacement across 46 countries, with the number inventory, SIP connectivity, and compliance infrastructure to support that transition from a single wholesale relationship.
What is the PSTN and why is it being retired?
The PSTN (Public Switched Telephone Network) is the global infrastructure of copper lines, circuit switches, and physical exchanges that has carried telephone calls for over a century. Every traditional landline phone call, every ISDN circuit, every analog fax line runs over this network. It was built for a world where a dedicated physical circuit per call was the only way to guarantee voice quality.
That world no longer exists. IP networks carry voice more efficiently, at lower cost, with greater flexibility and with better monitoring capabilities than copper ever allowed. The result is a globally coordinated decision by national carriers and regulators to decommission PSTN infrastructure on defined timelines, market by market, and replace it entirely with IP-based voice.
The transition is structural and irreversible. Staying on PSTN in 2026 is not a neutral decision. In the UK alone, providers implemented phased price increases of 20% in April 2026, a further 40% in July 2026, and a final 40% increase scheduled for October 2026, specifically to accelerate the remaining migration from copper infrastructure.
Where is PSTN being switched off?
The timeline varies by country but the direction is consistent. Several major markets have already completed or are approaching their final switch-off dates:
- Germany, Netherlands, Estonia: PSTN fully decommissioned. As Continuant’s global PSTN switch-off map documents, these countries have already turned their PSTN off and replaced it entirely with VoIP infrastructure, while Denmark plans to complete the transition by 2030 and Japan by 2028.
- United Kingdom: Final PSTN switch-off scheduled for January 31, 2027. According to TelcoBridges’ technical guide on PSTN migration, Openreach stopped selling new PSTN and ISDN lines nationally in September 2023. Enterprises still on copper are in active migration.
- Australia: Legacy copper PSTN progressively decommissioned as services migrated to the National Broadband Network (NBN), with that transition substantially completed through 2025
- United States: No single national switch-off date. The FCC’s technology transitions framework allows carriers to retire copper and TDM facilities on a service-by-service basis, making the US sunset a rolling series of carrier-level decisions
- Denmark and broader Europe: National carriers targeting full switch-offs by 2030
- Japan: NTT has been phasing out PSTN since 2010, with full switch-off planned for 2028
The pattern is the same across every market: carriers stop selling new legacy services first, then raise prices on existing ones, then set a hard cut-off date. Organizations that wait for the cut-off date face rushed migrations under deadline conditions, higher costs, and limited provisioning availability as engineering resources become constrained.
How does PSTN replacement work technically?
Replacing a PSTN connection does not mean replacing the phone number. It means changing the infrastructure that carries calls to that number. The number itself ports to the new SIP-based provider and continues to work exactly as it did before, from the caller’s perspective.
The technical migration involves three components:
- DID numbers: The phone numbers that were previously tied to physical PSTN lines are replaced with DID (Direct Inward Dialing) numbers provisioned over SIP. The same number, now routed through software rather than copper
- SIP trunking: The connection between the organization’s phone system and the carrier network. SIP trunks replace the physical ISDN or analog circuits, carrying calls over the IP network to the same destinations
- SBC (Session Border Controller): The network element that manages security, protocol translation, and the handoff between the organization’s internal VoIP infrastructure and the carrier’s SIP network
For organizations running on a PBX or UC platform, PSTN replacement is primarily a number porting and SIP trunk configuration exercise. The internal system continues to operate. What changes is the carrier connection underneath it.
What happens to existing numbers during PSTN replacement?
Number portability is central to any PSTN replacement project. The established business numbers, whether local geographic numbers, national service numbers, or direct line numbers that employees and customers already know, carry significant practical value. Losing those numbers during a carrier migration is an avoidable business disruption.
In most markets, number porting from a legacy PSTN carrier to a SIP-based DID provider is a regulated right. The process transfers the number without changing its format or geographic identity. The caller in London still dials the same London number. The call now terminates over SIP rather than copper.
Porting complexity varies by market. Numbers sourced directly from the carrier holding the original numbering authority allocation port more predictably than those that have passed through multiple intermediaries. For organizations with large number inventories across multiple countries, porting coordination requires a wholesale partner with documented per-market porting processes, not just general connectivity. For more context on how DID number porting works at the wholesale level, see How the Wholesale DID Market Works.
C3ntro Global DID coverage for PSTN replacement
While C3ntro Global’s DID number inventory spans 120+ countries overall, PSTN replacement deployments require additional infrastructure, including number portability rights and per-market regulatory compliance, that C3ntro Global currently supports in 46 of those markets. Every number in the inventory includes PSTN replacement capability, with portability available in the markets where regulatory frameworks support it.
The coverage spans the full range of number formats relevant to enterprise PSTN replacement deployments:
- Fixed geographic numbers across all 46 markets, preserving local area code identity through the migration
- National numbers in markets where organizations need a single number for country-wide reach
- Mobile numbers in markets including Mexico and Nicaragua, for deployments that extend beyond fixed-line replacement
- SMS-enabled numbers in markets including Costa Rica, Mexico (mobile), and Peru, for organizations that need dual-channel voice and messaging on the same number
For organizations managing PSTN replacement across multiple markets simultaneously, C3ntro Global’s platform provides unified provisioning, single commercial relationship, and compliance infrastructure per country through one wholesale partner. For more on how DID infrastructure works in enterprise deployments, see What Are DID Numbers? and How Do DIDs Work?
Frequently Asked Questions
What is PSTN replacement?
PSTN replacement is the migration of voice connectivity from legacy circuit-switched telephone infrastructure (copper lines, ISDN circuits, analog exchanges) to IP-based voice delivered through SIP trunking and DID numbers. The process preserves existing phone numbers through number porting while eliminating the physical infrastructure underneath them. PSTN replacement is being driven by national carrier decisions and regulatory timelines across more than 30 countries, with major markets including the UK, US, Australia, and most of Europe at various stages of their switch-off programs.
When is PSTN being switched off?
Timelines vary by country. Germany, the Netherlands, and Estonia have already completed their PSTN decommissioning. The United Kingdom has a final switch-off date of January 31, 2027. Australia substantially completed its copper-to-NBN migration through 2025. The United States operates on a rolling carrier-by-carrier basis with no single national deadline. Denmark and other European countries are targeting full switch-offs by 2030. Japan plans to complete its transition by 2028. In every market, the pattern is the same: new legacy services stop first, prices on existing services rise, then a hard deadline is set.
Can I keep my existing phone numbers when replacing PSTN?
Yes, in most markets. Number portability allows organizations to transfer their existing geographic and national phone numbers from a legacy PSTN carrier to a SIP-based DID provider without changing the number itself. The caller experience is identical: they dial the same number and it connects as before. The difference is that the call now routes over SIP rather than copper. Porting timelines and complexity vary by country and by the sourcing tier of the provider. C3ntro Global supports number portability in the markets within its 46-country DID coverage list where regulatory frameworks permit it.
What is the difference between PSTN and SIP trunking?
PSTN uses physical copper circuits where each call requires a dedicated line for its entire duration. SIP trunking uses virtual connections over IP networks where multiple calls share infrastructure, scaling to concurrent call volume rather than physical line count. SIP trunking is the standard replacement mechanism for PSTN: the organization’s phone system connects to the carrier via SIP instead of a physical circuit, and DID numbers replace the geographic numbers that were previously tied to those circuits. The result is lower cost per call, faster provisioning, and the ability to route calls to any IP endpoint in the world.
What is a DID number and why does it matter for PSTN replacement?
A DID (Direct Inward Dialing) number is a phone number provisioned over SIP that routes calls directly to a configured endpoint without a dedicated physical line. In a PSTN replacement context, DID numbers replace the geographic numbers that were previously tied to copper circuits. The number format, area code, and local identity are preserved. The underlying infrastructure changes from physical to software-defined. C3ntro Global provides DID numbers for PSTN replacement across 46 countries, with fixed geographic, national, and mobile formats available depending on the market. For a full technical explanation of how DID numbers work, see How Do DIDs Work?
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