Adding my land line to my Comcast account (have Comcast Internet and TV equipment)

Voice, Internet and TV are included on my bill. I have Comcast WiFi for computer and Comcast box for my TV. The Voice number Comcast assigned to my account has never been used. Can it be used for a telephone land line? Or just a mobile phone? 

If that assigned number is not for a land line, how much is a land line per month and how do I switch?