Migration from legacy PBX and hosted VoIP to modern cloud telephony — numbers ported on a scheduled date, call flows rebuilt, old system retained until proven.
The inventory is the project
Phone migrations do not fail on technology. They fail because something was connected to the old system that nobody remembered.
The list that catches people out is consistent: a fax line still receiving from one supplier, an EFTPOS terminal on a dial-up backup, an alarm dialler, a lift emergency phone, a back-to-base monitoring line, a direct number printed on signage or a vehicle, and at least one number that rings somewhere nobody can identify.
Every one of these needs a deliberate decision before anything moves. Some transfer straightforwardly. Some — lift phones and alarm lines particularly — often should stay on a separate service for sound safety reasons rather than being forced onto VoIP.
Rebuild the call flows, do not copy them
The call flow in a ten-year-old PBX is an archaeological record. Rules added for a person who left in 2018, a queue that overflows to a department that no longer exists, an after-hours message recorded by someone nobody recognises.
Copying it into a new system reproduces every accumulated oddity and wastes the one moment when changing it is easy.
Migration is the point to ask what should actually happen: who answers first, what happens when they do not, where after-hours calls go, and whether the IVR menu is helping anyone or just making callers press four buttons to reach reception. That conversation belongs with the people who answer the phones, not just with management.
Parallel running
The new system is built and tested while the old one carries live traffic. Problems surface during testing rather than during cutover.
Porting is scheduled with the losing carrier and is usually the longest lead time in the whole project — typically a few weeks, and largely outside anyone’s control. The old service stays active until it completes, so there is no window without calls.
What it usually saves
Legacy line rental is generally higher than the cloud equivalent, and the PBX hardware maintenance contract disappears entirely. For many businesses the ongoing saving covers the migration cost within the first year.
The less quantifiable saving is losing the dependency on the one technician who understands your specific PBX and is increasingly hard to get hold of.
When not to migrate
If your system does what you need, is still supported, and the numbers do not favour a change, keep it. Extending an existing PBX with VoIP trunking is a legitimate option where the hardware has useful life left.
The things that genuinely force the issue are end-of-life hardware with no support path, carriers retiring the underlying services, and remote working being impossible. If none of those apply to you, we will say so.