Kindle for iPhone and free books

I recently downloaded a Kindle for iPhone and the Barnes and Noble E-Reader as I am attending to get either a Kindle or a nook sometime in the near future and I wanted to get an idea of what to expect.

After downloading the Kindle for iPhone, I downloaded a book being offered on Amazon for free until X date.

So my question is:
1) Are the "free books" mine forever? Or do they get deleted after X date passes?
2) If the books are mine forever, can they be deleted from the iPhone or real Kindle and then retreived again later?

1. The books are yours forever
2. You can archive them and call them back whenever you want. I have done this a few times.

Interesting. I assumed (because of the lack of screaming about withdrawn offers) that was the best interpretation, the wording threw me.