You need to sign up with national do not call list. Comcast does not maintain this list. Google on "national do not call" and you should be able to find out how to register.
Bob Caswell Rajesh, I already had signed up for that list minutes after I received my new phone number. The do-not-call list is a totally separate issue, though. Bottom line: solicitors still get my new number (whether or not they call it is a different issue) unless I pay Comcast.