To give callers the ability to transfer phones calls directly to another callers Voice Mailbox in CUCM is quite a simple process, however it comes with a couple of gotchas that may have you pulling your hair out.
Start by first creating a CTI Route Point (CTI RP), this CTI RP will never register with an application or device, this is purely just to direct the calls to Voicemail.
So go to Device and CTI Route Points
Click Add New Device and complete the general details as you would normally, including Device Pool, MRGL, Location, CSS etc. CLick SAVE.
Now you will see Line [1] appear at the bottom of the page. This will where we will create a new line/DN. So click on Line [1]. BTW we can configure multiple Lines on a CTI RP.
I prefer to user # as a prefix for Transferring Direct to VoiceMail. In the Directory Number Field enter #XXXX (In this example Im using a 4 digit numbering plan, if you were using a 6 digit numbering plan place 6 X’s so #XXXXXX)
Give the Line a Description and Alerting Name.
**This is the gotcha. In the Alerting Name Field, Do Not include the word Voicemail. Even though CUCM will send the right digits in the right format and in the right fields ie last redirecting party number. However CUC will not treat this as a forwarded Call, but as a Direct Call, hence the caller will only hear the Opening Greeting for CUC.
Tick the Call Forward ALL check box and SAVE.
Now you call dial #(extension number) and the call will be directed straight through to Voicemail.