The key to turning this calming reflex on is the 5 S's: Swaddling, Side (or stomach), Shhhh, Swinging and Sucking. If you can figure out how to do these things correctly (because there is, to an extend, a right and wrong way to do it) you'll have some great comforting tools at your disposal, especially for colicky babies. I'll go over theses in greater detail in a future post.
I find The Happiest Baby on the Block a little long for a sleep deprived and overhwelmed parent (I say this having read this when my oldest was a colicky newborn!). There is a DVD of this book available that is a good substitute for this book and a lot quicker to learn from. Plus, I find it is easier to learn how to do something by watching someone do it rather than reading how to do it.
While I've heard amazing stories about a baby going from endless crying to content and happy with this book, it doesn't always happen as magically as that. So don't feel too frustrated if results don't come as easily to you.
Also, the main complaint I hear over and over again about the 5 S's is that after a few months the magic ends. Then you are left with a baby that has no idea how to sleep on his own and is addicted to sleep props. So be aware of this. Of course, when you've got a baby that you can't get to stop crying and that won't sleep you aren't really thinking about what problems you may end up with in 3 months, you just want something to help you and your baby NOW.
If you're interested, here's the book's facebook page: