You always have to pay the principle off in full, so I'm not sure how you can pay $44,000 less in interest and yet save a total of $138,000 in payments. But my main comment here is that this is a good idea if you don't have a better investment for that money. For instance, if you have any credit card debt at more than 4% (the mortgage rate), then you should be paying that off first from what I can tell, because that interest will be accumulating faster than what you're saving with the house interest. Likewise, if you can earn more than 4% elsewhere (or believe you can), same sort of thing.

On the other hand, in an age of economic uncertainty and people losing their homes, there is a secondary value to just getting the house paid off in spite of other opportunities, so this is something someone needs to consider for themselves.