I added a line to my house and they put a special box on and checked out the line(s) already going in, etc. But then I could at least argue with them if there was a problem as I could take a handset outside and test the lines, make sure it was the lines that had a problem. Our phone company charges a whole lot extra if it's inside the house, the wiring in the walls or something that's wrong. We were lucky because our house was custom built for its owner from the ground up and they did things well and right (except the finishing which they did themselves, it had a really ugly kitchen the father-in-law did out of not very high grade plywood but we eventually replaced the kitchen completely :-)