Planning a Legacy PBX Migration Without Downtime

Start With the Numbers

Number porting is the long pole in any migration. The carrier needs a clean application — exact number ranges, the current provider, a recent bill — and then a lead time measured in weeks. Everything else waits on the port date, so submit it first.

Build in Parallel

The new IP PBX is installed, configured and tested alongside the old system while the old lines still carry live calls. Extensions, IVR menus, ring groups and voicemail are all built and dialled through internally before cutover, so go-live is a switch-over, not a build.

The Cutover Window

• Schedule the port for the start of a quiet period — after close of business, ideally into a weekend
• Keep the old system powered and reachable for a few days as a fallback
• Use a temporary divert on the main line so no call is lost during the switch
• Have an engineer on site the first working morning after cutover

Reusing What You Have

Analogue handsets, door phones and fax machines can often stay, connected through an analogue gateway (ATA). Digital proprietary handsets from the old system usually cannot — budget for IP replacements for those desks, and redeploy the analogue kit where it still serves.