How do I set incoming calls to go directly to my VoIP voicemail?
This article explains how a person can send incoming calls the their VoIP voicemail
Press the "CFwdALL" softkey on your phone. Enter in extension 2222 if you have Asterisk voicemail, or 4000 for Unity. All incoming calls are now going directly to your voicemail. Pressing the "CFwdALL" softkey on your phone disables call forwarding. Note that if you have a Cisco 8800 series phone (with a color screen), you will have to forward any additional lines separately, as that model can selectively forward a single line at a time.