this should be easy...

we have 2 extensions that do not ring when outside calls are dialed. but internal 'intercom' does work. is there a way to get these two phones out of "do not disturb" mode? I do not know how and do not have any manuals.

They are "vodavi infinite" 12 button phones...i.e. they have 12 programmable buttons on top, no LCD display.

Thank you!