Ralph,
Lets stick with your logic being xxxx is the internal number and yyy-yyy-yyyy is the external number.
If I dial the speed call number xxxx from internally it does its job and forwards to yyy-yyy-yyyy, if the user does not answer it will go to the yyy-yyy-yyyy external voicemail
From my cell phone, if I dial the businesses main number where the auto attendant asks to enter an extension, I enter in the speed call number xxxx, it sounds like it does its job as the line will start ringing (assuming its dialed yyy-yyy-yyyy) but eventually loops back to the auto attendant before yyy-yyy-yyyy's external voicemail picks up
I need to get yyy-yyy-yyyy's external voicemail to pickup if they dont answer when external people call in.