I have Comcast, and the service is generally reliable with one HUGE exception:

Every couple days or weeks, as I'm speaking on the phone (I have voice-over-IP via a third-party provider, like Vonage or Lingo), my Comcast connection begins to slowly cut me off. First, the person on the other ends stops hearing me. Eventually, the call is lost altogether, and I have to reboot the modem.

I thought it was just me until the other day, when I was speaking to a co-worker, who lives in a completely different area of the city, who had the exact same problem.

So, anyone else out there notice that Comcast seems to cut off calls when you're using a competitor's VOIP service?