There are three Cisco IP phones configured for a location. The customer doesn't want Cisco Unity voicemail configured on any of these devices. The customer wants that a Cisco Unity voicemail should be configured on a Dummy device. The call settings on the 3 Cisco IP phones like No Answer Internal/External should be forwarded to the voicemail of that dummy device.
The problem is that if you directly call the Directory Number of dummy device, the voicemail box works but if a call has been forwarded via any of those 3 Cisco IP phones, the voicemail doesn't work.
I hope that someone can help me to sort out this issue.