PSTN to VoIP migration — step by step

PSTN to VoIP Migration: Step-by-Step Guide

A practical migration process for UK businesses moving off legacy phone lines

Use this page to move from audit to cutover in a controlled way. It explains how to migrate from PSTN to VoIP without turning the project into guesswork, and keeps the focus on scope, number planning, testing, continuity, and go-live control.

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Detailed timeline and guidance for the UK PSTN to VoIP migration, highlighting routing for business continuity and risk mitigation.

Process-first migration

Audit first, then scope, then numbers, testing, and go-live control. This page is the execution layer, not a provider shortlist or comparison page.

How to use this guide

Use the checklist to document the live estate, then follow this guide to run the migration in the right order. Keep the PSTN hub for broader readiness context and continuity planning.

Start with the live line and dependency audit
Use this page for sequence, control, and migration decisions
Use the quiz and savings tool only after scope is clear enough

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What this guide is — and what it is not

This is the migration process page. It explains how to switch from PSTN to VoIP in the right order, how to reduce continuity risk, and how to plan numbers, devices, testing, and fallback routing. It is not a provider ranking or comparison page.

Start with checklist Open PSTN hub

PSTN to VoIP migration process

This is the core sequence. Treat it as the control path from audit through stabilisation after go-live.

Audit the live estate

Document every line, number, service, dependency, supplier, and owner before making migration decisions.

Main numbers and DDI ranges
Analogue or line-dependent services
Site-level ownership and criticality

Define migration scope

Separate critical services from standard services and special-case dependencies so the project can be sequenced properly.

What must not fail
What can move in phases
What needs separate remediation

Choose the right migration model

Decide whether the business needs a full cutover, phased rollout, or hybrid transition based on risk and complexity.

Single-site cutover
Multi-site staged migration
Mixed legacy and modern environments

Check connectivity and resilience

Confirm the network, internet access, and continuity arrangements are strong enough to support business calling.

Connection stability
Power and outage planning
Fallback communication paths

Plan numbers and call flows

Map which numbers stay, which numbers retire, and how inbound and outbound call handling should work after migration.

Porting preparation
Main number routing
IVR, hunt, overflow, voicemail

Prepare users and administration

Make sure devices, permissions, user setup, internal owners, and support contacts are ready before cutover.

Desk phone and softphone setup
Admin and permissions model
User guidance and support route

Test before go-live

Test real business scenarios, not just dial tone. The goal is operational confidence, not technical assumptions.

Inbound and outbound calls
Transfers, voicemail, routing
Remote and mobile workflows

Run a controlled cutover

Use a defined go-live window with named owners, escalation contacts, live checks, and fallback actions.

Main number verification
Supplier escalation path
Continuity protection during change

Stabilise and optimise

Review issues, correct routing gaps, improve user setup, and refine the new environment once the service is live.

Post-go-live issue review
Workflow optimisation
Reporting and admin refinement

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What to lock down before cutover

These are the areas that usually decide whether go-live feels controlled or chaotic.

PSTN switch-off readiness planning for UK business migration projects.

Numbers and call paths

Know which numbers are being retained, which numbers can retire, and exactly how inbound routing should behave once the new system is live.

Business checklist

PSTN to VoIP migration planning with audit, porting, and testing steps.

Testing and sign-off

Do not rely on basic connectivity tests alone. Use real business scenarios and decide in advance what must pass before go-live is approved.

Open PSTN hub

VoIP migration planning with cost visibility and cutover preparation.

Fallback and stabilisation

A migration is not finished when the system switches on. Keep fallback routing in place and review issues, user setup, and routing behaviour after cutover.

VoIP savings calculator

When phased migration is safer than a fast cutover

A full cutover can work for smaller, simpler environments. But a phased approach is usually safer when the business has multiple sites, mixed dependencies, complex numbering, or low tolerance for interruption.

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Strategic planning graphic for the UK PSTN switch-off in 2027, featuring readiness routing and business continuity safeguards for VoIP migration.

Starting with provider choice too early

If the audit is weak, the shortlist is often built on incomplete assumptions instead of live service reality.

Leaving number planning too late

Main numbers, DDI ranges, ownership details, and routing logic should be reviewed early because they often carry the highest continuity risk.

Skipping fallback control

Go-live should always include named owners, escalation contacts, live verification order, and continuity protection if the expected behaviour does not hold.

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Frequently asked questions

Common questions about how to switch from PSTN to VoIP, how to plan cutover safely, and what to review before go-live.

The first step is a full audit of the live estate. That means lines, numbers, connected services, dependencies, sites, suppliers, and internal owners. Without that, the migration plan is usually incomplete.

No. A phased migration is often safer for multi-site businesses, mixed estates, complex numbering structures, or environments with low tolerance for interruption.

Early. Number continuity should be planned near the start of the project because main numbers and published contact routes often carry the highest continuity risk during migration.

Test inbound and outbound calling, transfers, voicemail, routing, user login, softphone access, remote workflows, and the main business call scenarios that matter operationally.

That is why a fallback plan matters. A strong go-live plan defines escalation routes, fallback call handling, verification order, and who makes decisions if the new environment does not behave as expected.

Use the quiz once the audit and migration scope are clear enough to understand what kind of solution the business actually needs. It should support the migration plan, not replace it.

Next step

Turn the audit into a controlled migration plan

Start by documenting the live estate properly, then use the quiz to tighten solution fit and the savings calculator to sense-check likely commercial change.

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