I am using an Aastra 57i as a receptionist phone and have an extension # set up for it. I can use lines 1 - 4 with no problem. Lines 5 - 9 don not always work, is there a solution for that? also if i am currently on any of the lines when a new call coem in to the receptionist i get a line busy signal. Is there a way so that the receptionist can have notifications for all the lines when needed?