My Norstar M7310 has a different VM message for lines 2 thru 5 when line 1 is busy. How do I get that message to be the same as the message for line 1, which is a custom recorded after-hours VM message for my company? The message for lines 2-5 is a voicemail recording for a person who is no longer employed at our company, and his extension is no longer in use.