Migrating an Enterprise Phone System: Verizon to Vonage
5,000+ numbers. 20+ offices. Zero disruption.
A phased, office-by-office cutover from a legacy Verizon system to cloud VoIP, with the IVR, the billing, and the call center all riding along.
20+ offices and a call center were running on a legacy Verizon system, with 5,000+ phone and fax numbers that needed to move to cloud VoIP without disrupting service.
The call center couldn't go dark, even for a minute, and neither could the fax lines still quietly running billing and compliance workflows in the background. Every one of those 5,000+ numbers had to land on the other side working, on a schedule that didn't interrupt the people using them.
Underneath the number-porting problem sat a second one: the IVR call-routing logic was complex, undocumented in places, and would need to be rebuilt and proven before a single office cut over.
A botched cutover doesn't just mean a support ticket. It means a call center that can't take calls, and a company that can't be reached. The margin for error was close to zero.
Ran a phased, office-by-office migration with live-tested IVR redesign and a shared billing dashboard to catch overlap charges before they happened.
Five things had to go right at once, across 20+ locations that don't run on the same clock.
- Porting 5,000+ phone and fax numbers with zero downtime on critical lines
- Migrating and re-validating complex IVR call-routing logic
- Managing overlapping Verizon/Vonage billing to avoid double charges
- Coordinating site readiness and legacy equipment disposal across 20+ locations
- Training staff on new phones and voicemail access before cutover
The number that mattered most here was never on the invoice: zero. Zero dropped calls the day of cutover, across every office. That's what phased planning and a shared tracking dashboard buy you: not a faster migration, a boring one.