# The business PSTN-migration audit

A PSTN migration starts with finding what the business depends on. Telephone bills describe purchases, while a site visit reveals equipment and working practices. Reconcile both before deciding which services to move, replace or retire.

18 February 2026

[Voice & PSTN](https://netavo.com/insights)

## Reconcile the invoice with the building

Start with the latest bills from every telecoms supplier, including local accounts paid outside the central IT budget. Record each telephone number, account reference, service description, installation address and contract contact. Compare those records with the phone system, the building manager's equipment list and the people who actually use each site. An unexplained charge or an unlabelled socket deserves an owner, not an assumption.

Walk the premises with someone who knows its operational systems. Reception phones are visible, but a line may also serve a lift call point, alarm panel, door entry system, fax machine or remote monitoring device. Trace the connection far enough to identify the equipment and its maintainer. Do not disconnect an apparently quiet line to discover what it does, particularly where safety or monitored signalling may be involved.

Keep evidence beside each entry. A photograph of the equipment label, a supplier invoice reference and a confirmed contact are more useful than a spreadsheet cell marked probably unused. Numbers advertised on websites, stationery and customer portals need checking too. A line may receive very few calls while remaining the published contact for an important business process.

## Give each dependency a decision and an owner

Create one inventory row per service or dependency, rather than one row per invoice. Include its location, number, connected device, business purpose, operational owner, equipment maintainer and current supplier. Add the proposed outcome, the person authorised to approve it, prerequisite work and the evidence required for acceptance. Where several devices share a service, record those relationships explicitly.

Use three clear outcomes: retain the function on a replacement service, replace the equipment and connection together, or retire the function with business approval. A replacement voice connection does not establish that an older device will operate correctly through it. Ask the equipment supplier to confirm the supported migration approach and a test covering the complete operational journey, including the receiving service where applicable.

Give specialist dependencies their own workstream. The [lift monitoring and call points sector page](https://netavo.com/sectors/lift-monitoring-and-call-points) and [fire and security sector page](https://netavo.com/sectors/fire-and-security) provide the relevant starting points. Treat these as planned engineering changes with the responsible maintainer, not as ordinary handset swaps. Keep unverified equipment compatibility visible as an unresolved decision, with a named person responsible for obtaining an answer.

## Build the critical path around acceptance

Sequence the migration from prerequisites to acceptance. A new access circuit, suitable local networking, equipment replacement, number transfer and staff training may involve different suppliers. Record who confirms each milestone and which later steps depend on it. An installation appointment is not the same as a tested service, and a requested number-transfer date is not evidence that every dependency is ready.

Define acceptance before the change. Ordinary business voice tests might include inbound calls to each important number, outbound caller identification, expected answering behaviour and operation from the actual desks or softphones people use. Specialist equipment needs tests agreed with its maintainer. Record the result, time, tester and any restrictions, then retain the evidence with the inventory.

Netavo provides [hosted telephony, SIP trunking and UK numbers](https://netavo.com/services/voice). These are building blocks for the voice part of a migration, alongside the wider planning described on the [PSTN switch-off sector page](https://netavo.com/sectors/pstn-switch-off). Confirm the proposed design against the inventory rather than treating a product selection as approval for every connected device.

After acceptance, reconcile the next invoices and check that retained numbers still reach the intended destination. Close redundant services only through an agreed supplier process, with dependencies checked first. The completed audit should leave the business with a current service register that can support future moves, changes and fault diagnosis.

## Common questions

### Can we use telephone bills as the complete inventory?

No. Bills identify purchased services but may not explain attached equipment, shared dependencies or how the business uses a number. Combine account records with physical checks and confirmation from service owners.

### Does a working handset prove an alarm or lift device will work?

No. Each connected device needs a migration approach and acceptance test agreed with its maintainer. Test the complete function, including the receiving service where relevant.

### When should an old service be cancelled?

After the replacement has passed its agreed tests and the supplier has confirmed the effect of cancellation on linked numbers and services. Keep written acceptance and cancellation records.

## Related services and sectors

### [Cloud Voice & Numbering](https://netavo.com/services/voice)

Hosted telephony, SIP trunking and numbering on our own platform, for a single user or a contact centre.

### [PSTN Switch-off](https://netavo.com/sectors/pstn-switch-off)

Cellular replacements for legacy PSTN voice and signalling applications, with cloud voice and alarm signalling.

### [Lift Monitoring & Call Points](https://netavo.com/sectors/lift-monitoring-and-call-points)

Cellular replacement for lift alarm and call point lines, and multi-network mobile data for lift monitoring.

### [Fire & Security](https://netavo.com/sectors/fire-and-security)

Signal Dynamic alarm signalling over up to four verified paths, for installers and alarm receiving centres.

## Plan the voice part of your migration

Bring your number inventory, site list and unresolved dependencies to Netavo so we can discuss the hosted telephony or SIP trunking requirements.

[Work with us](https://netavo.com/work-with-us)

Source: https://netavo.com/insights/pstn-migration-audit