Just thought I'd bump this instead of making a new thread, On my HTC One X I was able to long press the number in call history and add it to call barring without needing a third party app and you don't even know that you're even receiving the call (I looked at my carrier's call logs). There doesn't seem to be any way to block calls on the Moto X, so I'm looking for an app, I just installed root call blocker (I rooted the Moto X) so we'll see how it works.