Modern enterprises run on apps and APIs, but many still depend on older voice and connectivity layers that were designed for a different era.
The problem is not that legacy is bad; it is that it does not match today’s pace of change, remote work patterns, and security expectations.
In the UK, the government has been clear that the traditional Public Switched Telephone Network will be withdrawn, which forces organizations to treat migration as an operational priority, not an optional upgrade.
That shift tends to expose how much “critical comms” is tied to old lines, contracts, and assumptions.
What A Practical Transition Looks Like
A practical transition is less about ripping everything out and more about sequencing changes so the business keeps running. It usually starts with discovery, then a pilot, then staged migrations by site, system, or function.
A useful way to think about it is moving from “lines” to “services.” Instead of counting circuits, teams define what outcomes they need: inbound and outbound calling, conferencing, contact center routing, failover, and integrations with identity and CRM.
Key planning steps often include:
- Inventory every voice path, including “quiet” lines used once a quarter.
- Classify endpoints: softphones, desk phones, analog devices, and embedded telephony.
- Decide where call control lives: cloud, on-prem, or hybrid.
- Design resilience for the internet, power, and routing.
- Run parallel operations long enough to prove performance.
Hidden Dependencies That Catch Teams Off Guard
Many migrations stumble since voice is rarely just voice.
It is door entry, lift alarms, building management, fax, payment terminals, and legacy modems tucked into back offices. This is where the PSTN switch-off becomes more than a telecom milestone, since it forces teams to map real-world workflows that never made it into architecture diagrams. When you surface those dependencies early, you can assign owners, choose replacements, and avoid last-minute exceptions.
That mapping creates a shared language between IT, facilities, security, and vendors. A practical approach is to group dependencies into “replace,” “re-platform,” and “retire.”
Replace means swapping a device or service like-for-like, re-platform means moving the function onto IP or cellular, and retire means removing it entirely since nobody actually needs it anymore.
Resilience And Continuity In An IP World
IP-based communications can be more resilient than legacy lines, but only when resilience is designed on purpose. Enterprises need to treat connectivity like a utility: redundant paths, clear failover behavior, and tested recovery procedures.
One risk with legacy networks is that they can appear stable simply due to nobody changing them.
A parliamentary briefing noted that Ofcom estimated 5.2 million residential landline customers were still on the PSTN, which signals how large the remaining footprint is and why transition plans need to assume mixed environments for a bit.
In practice, continuity improves when you diversify failure domains. That might mean dual internet circuits from different carriers, cloud calling with geographic redundancy, and policy-based routing so critical traffic stays usable even during a partial outage.
Security, Compliance, And Observability Benefits
A modern transition is a chance to raise the security floor. Legacy telephony often sits outside normal monitoring, patching, and identity controls, which makes it easy to forget and hard to audit.
When voice and collaboration move onto the same governance plane as other enterprise services, you can apply consistent access control, logging, and change management. That matters for regulated industries where you need to prove who accessed what, when, and why.
Observability improves, too. With IP services, teams can monitor jitter, packet loss, MOS scores, and routing events, then correlate them with WAN changes and SaaS performance. That turns “the phones sound bad” into measurable data that can be fixed faster.
These controls reduce blind spots that attackers often exploit. Audits become simpler when records are centralized and standardized.
Security teams can respond faster because signals are visible in familiar dashboards. Compliance reporting shifts from manual checks to ongoing verification. Altogether, this creates a more resilient and accountable communications environment.
Measuring Success After The Cutover
A useful transition plan defines success metrics before the first site moves. Otherwise, teams end up chasing anecdotal complaints with no baseline to compare against.
Good measures include call completion rates, average time to restore service after incidents, the number of legacy exceptions still in production, and helpdesk volume by migration wave. If you track these per location and per user group, you can spot patterns and adjust the rollout.
The strongest indicator of a healthy transition is when communication becomes boring again. When users stop thinking about the network and start trusting it, you have not just replaced old lines, you have modernized a critical business dependency.
