In the end of the video he promised to break the phone on his next video, so maybe we see the metal hammer. Will be painful to watch..
I subscribed to that youtube channel just to see the final video. :)
Still, the suggestion to hit it with a real hammer is kind of moot, because he uses the phone as a hammer in the same video. There's a reason we don't see videos like this for the iPhone5 or S3, etc (well actually there are hammer test videos out there, but you'll notice the iPhone 5 and S3 break fantastically on the first or second hit).
I'm going to conclude that the Nokia Lumia 920 might actually be the most durable smartphone ever made.