There is a good app for "call blocking" in Play Store:
http://play.google.com/store/apps/details?id=com.vladlee.callblocker
For me, it's working! You can try it for yourself. Good luck!
http://play.google.com/store/apps/details?id=com.vladlee.callblocker
For me, it's working! You can try it for yourself. Good luck!