I have a Norstar 616 KSU / DR5. Ext 21 is set for prime line to be pool. When you lift the hand set it goes to the intercom button and in display reads "Line 04" if you dial it is intercom dial tone. There is no line 04 configured in system and when you do feature * 0 that button shows Intercom 21 / status port 101. I know it must be something simple but I just can make it work right. Thanks for your help in advance. This forum, and the folks who make it happen is so extremely helpful.