I feel stupid for asking this, but where is this power detailed in the PHB (ie page number)? I can't seem to find it anywhere. Thanks.

Page 130. The two paragraphs under the bold words are the pact boon.

The second last paragraph of page 130. Ninja'ed!

Hmmm.... I feel like I'm missing something. What are the mechanics of the Misty Step? I inferred that it allows a 3 square teleport, but is it At-Will, Enouncter, Daily?

It triggers when your party defeats an enemy that was under your warlock's curse. There's no limit to how often you can use it.

Misty Step(free action, when an enemy affected by your warlock's curse is reduced to 0 or fewer hitpoints; at-will)
You can teleport up to three squares.

It's a free action, actually.

Thanks very much!