Building Rollover Lines
Step 1: Navigate to the phones tab and add the appropriate extensions the the phone(s) that you need.
Step 2: Set up the Lines to roll over properly. In order to do this under option 2 Line Forwarding you'll need to set the Forward Busy/Forward No Answer/Forward Not Registered option to the next line you wish it to go to.
1000 - rolls over to extension 2000 if no one answers
2000 - rolls over to extension 3000 if no one answers
3000 - if no one answers it goes to an Auto Attedant.
Step 3: Make sure the last rollover line has some place to go. It is a good idea to have it go to an Auto Attendant or Voicemail.