IIRC, the originating party's on-hook will immediately disconnect the call, while if the receiving party goes on-hook, there is a short but significant delay be

IIRC, the originating party's on-hook will immediately disconnect the call, while if the receiving party goes on-hook, there is a short but significant delay before disconnect is finalized. This may have something to do with service offerings such as call-waiting and 3-way, which depend on detecting a "flash" signal.