Call them from one phone first and let it ring, then call them again immediately from a second phone while the first is still ringing. The SECOND phone should ring straight into their voicemail.
Wow......I feel like I just, like, totally helped a stalker......
;^) Clever solution. I wouldn't have thought of that.
:^/ Still, it begs the question why one would want this. Ususally, voicemail is only a backup to speaking to the other party. Maybe someone wants to call in sick or something without being talked out of it?