I fixed this by "copy settings" from another working ext. But I still don't know what made this happen. Ext 12 would ring(intercom) every 30 mins, when you pick it up it would rapidly dial 6 digits.. then dead. The intercoms also sounded like dial tone, even with no lines.
If you call another ext. from 12 it rings in as "voice messaging system".
What am I missing?

You had it assigned to the voicemail hunt group. The system calls up the first extension in the group every 30 minutes to sync the time and date, and everytime you press the Night Service button. The touch tones you heard are "mode codes" that communicate from the ACS to the voicemail. The intercom sounds like outside dial tone because some outboard voicemails "listen" for dial tone before dialing, and are confused by internal dial tone.

Thanks, didn't think it was any vm issue because all I did was 'copy settings'.