The situation

A multi-site real estate group ran three bridged 3CX systems, one per office, each behind its own edge firewall. All three v18 licences were set to expire at midnight on 30 September 2025. The mobile app had already been deprecated on v18, and one site had been failing the 3CX Firewall Checker for months, which showed up on calls as one-way audio and dropouts. Losing telephony in the middle of a busy season was not an option.

What we did

Renewed the licences first. All three were secured roughly twenty minutes before the deadline, which took the outage risk off the table before any other work started.

Backed everything up. Hyper-V snapshots and full system exports for each PBX, with the rollback procedure tested rather than assumed.

Upgraded all three together. Because the systems were bridged, they had to move as a set. We ran the v18 to v20 migration in one 7pm ET cutover window, roughly five hands-on hours, entirely off-hours.

Fixed the firewall properly. We audited the NAT and port configuration at the failing site and corrected it. The 3CX Firewall Checker passed on the first retest.

Handed over the documentation. Annotated diagrams, a change log and an audit checklist, so the next person to touch the system is not starting from nothing.

The result

• No service interruption during the cutover.
• All three systems live on v20 with the bridges working.
• The firewall fault resolved and the call drops gone.
• Written documentation in place for future maintenance.

AtoZinIT renewed our expiring 3CX licenses in minutes and upgraded three bridged systems to v20 the next night. They also fixed a firewall issue our team had chased for months.
— Victor, MSP IT Lead