I think I used to take a phone and tie it to an ext. that wasn't being used and then set that ext to cfwd off net. Then take the phone and put it back where it came from. Program a button for the phantom ext. and when a call came in for the cell phone just transfer to that ext. But I'm getting old. I know you can do that with the single line ports, but I don't know how many cell phones you need to transfer to.