I think it needs to appear only, it reads from the stuttered dial tone and yes it has to do with caller ID because the message center phone number sends the signal, nortar then recognizes that number you programmed then sends the signal to the set. This may differ between Canada and the U.S..
In programming look for Ext Vmsg, option 9 / Admin in older software?.
Newer software:
Telco Features – Show
VMsg ctr tel#s – Show