We are running call manager 5.1. Today at our corporate office we use 3 digit ext. and need to switch to 4 due to over lapping numbers with branch offices having 4 digits. One question that has been asked is we will know if someone is on their line if we go to 1 extention on a phone. Today each person has a 3 digit primary ext and a 4 digit secondary ext. If the primary 3 digit if busy it rolls to the secondary 4 digit number. This way if I call someone and they are on the line I can tell becuase it rolls to their second line. Is their notification that would tell me someone is already on their line if we switch to single ext's at each phone.