Find out what can stay
Begin with an inventory: PBX model and software, extension types, carrier connections, handset models, cabinet condition and cable records. Mark faults that already exist so they are not confused with migration issues.
Give every item a decision: retain, test further, replace now or replace in a later phase. Compare the cost of adaptation and ongoing support with replacement; retaining everything is not automatically the economical option.
Choose a transition you can control
A single change window may suit a small, well-documented system. A staged change may suit several buildings or a refurbishment programme. Connecting old and new systems temporarily is only useful when the interfaces, call capacity and dialling behaviour have been tested.
Write down who approves each stage and what must work before the next group moves. Keep a tested means of reaching reception during the change, and tell staff exactly which procedure to use.
- Test a representative room, reception handset and external call route.
- Confirm number-transfer or carrier-routing arrangements directly with the provider.
- Schedule access with front office and engineering, including a stop-work decision.
- Record the point at which the old configuration can no longer be restored easily.
Treat fallback as part of the work
A fallback plan needs a trigger, an owner and a practical method: for example, restoring a saved configuration or keeping an agreed temporary route available. Simply leaving the old PBX in a rack does not establish a working fallback.
No migration is advertised here as having zero downtime. The proposal should describe the expected interruption, remaining risks, test criteria and the handover your team will receive.
Implementation walkthrough. Equipment reuse and parallel operation depend on the existing system and must be checked.