That sounds like the problem I had a few months ago. The problem was lightspan. The lines come out of the central office on fiber and are switched to copper somewhere near your site. I had 4 cos and only one of them had those symptoms. I had the verizon tech switch the co over to a regular pots line from central office and it worked. I have installed a Xts in the past and the comcast dial tone didnt have loop supervision. So the Xts wouldnt hang up. Guess we will see cause the customer bought the system!