I don't have either one, so I hope others will chime in..

For the phone ringing or not, have you tried changing the # of rings on the phone itself?
I think if you join & log on to the comcast website - you can set # of rings for the voice mail too. Maybe one of those is the problem.
My parents have a comcast package so I explored the site and settings when they got it set up.
But they haven't had any troubles.