i have an AT&T phone and its not free after 9 because i dont exactly have a contract its a go phone so depends on if they have a contract or not. and if they have the unlimited nights and weekends packages.
the individual cell phone plan with only 450 regualr minutes isnt free after 9 but does give you 5000 night and weekend minutes.
http://www.wireless.att.com/cell-phone-service/cell-phone-plans/individual-cell-phone-plans.jsp?_requestid=454717