Supported phone systems

The short answer

RingCentral and JustCall use the direct connection route. Dialpad and Zoom Phone use the call-side route while runtime verifies the available messaging path. CallRail requires supported secondary messaging. Quo / OpenPhone connects now, but provider-dependent work waits for a real completed-call event. An exact successful account connection may proceed to payment while the capability probe continues in the background. Provider support never substitutes for checking the connected account.