I have a similar problem. I have a Netgear purchased modem, not from Comcast. Been working fine for months. Now any incoming call (message or not) causes the modem to at least partially reboot (most lights go out, and they start blinking one by one, just like a normal reboot). Answering the incoming call gets dead air. On the other end, the caller hears the phone keep ringing and gets switched to voice mail.
Outgoing calls work fine. If on a call, call waiting works. But, answering kills the modem.
So, after any incoming call, no internet, no dial tone, until the modem restarts.
Went through level 1 and level 2 troubleshoot. Confirmed the issue, but can't say why it is now happening. My next step is to go get another modem and see if that fixes it.
There are a few other posts with detailed discussion on changing settings, and hacking the default way the device is supposed to work. Most of these don't seem to work.
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