Using third party SIP phones (basic) with CallManager 5.1.3
The phones have their own built-in DND feature. Basically, when you activate the phone's Do Not disturb, they respond to all incoming call attempts with a SIP 480 "temporarily Unavailable" message.
The expected behavior is that the callmanager would see this message and then forward the calls to voicemail based off the line configuration. However, instead, it appears that the callmanager just drops the call and plays fast busy to the caller.
Does anyone know if that is the correct behavior that the callmanager is expected to do on a 480 SIP response? Previously we were using these same phones with some different SIP PBX vendors and they had no problem forwarding the call to voicemail on a SIP 480 message.
Checked that the callmanager is properly configured to forward the call to voicemail on no answer, busy, no coverage, cti failure. Verified that on a no answer situation, the caller does indeed get forwarded to voicemail; so it appears that the voicemail profile is configured correctly.