Yes,  to my way of thinking, its a relfex, meaning you can use it at will, even if its not your turn.  But you still have to activate it, as it cost one power per turn to use.

would you have to shell out the 2 PR if it isnt your turn?

LOL, Heston!   

I've never viewed Willpower as something one "activated", because to me each of the defenses that activate spell out that specific word ("activate") out in their description.  So when my character Compass starts to enter the villain's lair, he will specifically choose to "activate" his Magnetic defense (and I tell the GM ahead of time, or it isn't considered "up" and ready).  We've never had a character about to enter a spooky cave "activate" their Willpower.

For Willpower, it's more of a character making a choice (there and then, when needing it), at least the way I've always viewed it.

Here's how we play the power now, based on whether the character knows about the attack or not (my players came up with this as a compromise):

Willpower: (p. 21)
Type (A): If the character is surprised by an attack, then they may not use Willpower as a defense; however, the damage scored by such a hit is halved when calculating their chance for unconsciousness.