Comcast's new xfinity modem does not support my home’s 4-phone (from 2 bases) and home alarm telephone system. The old modem supported the system just fine. When I connected the new so-called high speed xfinity modem, the Internet and TV worked fine. However, the phones and home alarm telephone communication did not.
Interestingly, when I directly connected only one phone to the new modem, it worked fine. So, I originally thought that somehow my internal home phone wiring had broken about the time I installed the new modem. To check that, I deactivated the new modem and reactivated the old one. Doing that solved the problem. The phones and alarm communication once again worked fine with the old modem.
But the process was painful. Comcast agreed to convert back only after a long (over one-hour) dispute with a technical rep, who refused to believe the new modem could be at fault, had me try all kinds of things, and then told me the new modem could not be deactivated. I checked my home phone wiring and found no problems. The next day, I called back to get a different rep, who had not problem deactivating the new modem and enabled me to reconnect the old one.
Comcast's new modem clearly has a serious design flaw.
Monetary Loss: $1000.