iOS 7 now includes built–in support to block calls, messages and Face­Time calls from anyone.

In iOS 7, call-blocking is available in the Phone app by going to the contact details screen via the Favorites, Recents or Contacts tab. From there, hit the Block this Caller button at the bottom. This will block not only phone calls, but FaceTime calls and messages from that person as well.

No third–party apps needed