The text blocking feature that Levi4u provided is available, but the call blocking feature has been delayed. Sprint is working diligently to get this feature implemented soon. As soon as I have additional information, I will post it in the Phones & Devices forum and we'll also ensure it's posted in the Services & Features forums.
Effective *Monday August 30*, Sprint customer care can assist you with requesting incoming or outgoing call blocks. Up to 50 phone numbers can be assigned to the block list. This feature is separate from the current text-blocking capability. (http://support.sprint.com/support/videos/Services_