Use the Extra-Dimensional Ghost Revealer at the entrance to Stratholme and speak with the ghost of Anthion Harmon.
Very well, [player]. All that remains is to put the goblin's invention to the test. Word has it that Anthion was slain by the undead legions of Stratholme as he tried to enter its gates.
Try using the device there and see if, indeed, you can speak with the dead!