Not sure if anyone else encountered this issue, but after two months (since 10/27/17), both inbound and outbound calls from landlines were fine. But every time a cell call was received, it dropped it about 3 seconds. I checked every setting, searched the web for a few hours, and could not find a solution or where this was a recent common issue. So as a last resort (before starting a Comcast chat or support call), I switched the Tele 1 and Tele 2 jacks in the back of the router/modem, and now the issue went away. Of course, I cannot make sense of why that resolved the matter, but I wanted to post this in the rare event someone else experienced the same issue.