Well your right about MMC 306. It is also the only place in the Samsung system where you can assign an off hook select. I would check the fax machines to see if they have some sort of off hook dial 9 programing. Also have you tried a butset connected directly to one of the analog ports. If you go off hook on your butset does it put you on a trunk or do you have intercom dial tone? This would rule out the Samsung as the culprit.