Watching the Red Sox / Atlanta game recap and noticed that the catcher has an earpiece.

[Wounded Bear]

6. Well, they usually say that the catcher "calls" the game...

but yeah, he looks to the bench quite often before he does.

The electronic communication is totally on the field between the players, unlike in football. At least that's how it is supposed to be. But you often see the camera cut to the bench and the manager or one of the coaches is touching his chin, nose, ear, etc in sequence, obviously some kind of signal.