In the AA menu, select touch tones, then add zero.
Connect the zero action to for instance a transfer action. In the transfer action specific tab, enter the user number to transfer to. By pressing zero in that menu, you go to the operator for that menu. Mailboxes have their own zero(operator), and the system can have a zero hunt groups, or a zero user as well, or a short codes zero that forward to a destination as well.
WHich zero(operator) were you talking about?