In the voicemail tab of the user.
Voicemail Reception: Default = Blank
When connected to a User's Voicemail the caller can press 0 to be transferred to either an internal number or external number. Enter here the telephone number to be used. The User should announce this facility in their greeting message, for example "John Smith is not available today, you may leave a message or press 0 for Reception".
Greets Peter