We have 4 POTs and if all lines are busy, the general mailbox would not pick up, so it will keep ringing. But the real problem is if they call line 1 when it is busy, the merlin magix system would not pass it to line 2/3/4 when they are free. Is there anyway to program the system so it will go to an open line so we wouldn't miss a call. Lastly, can this be done with a ETH-18D phone?