The 2008 nav systems that work with bluetooth are the cars already equiped with sync. If you want bluetooth to work on your 2007 edge with the nav system, you could buy mobile-ease, but that is VERY expensive, plus it is not entirely integrated as it has a separate control pod.
Id suggest checking out a parrot bluetooth kit, I am going to get one very soon. If you get a harness adaptor then it will plug right in, it also has a screen for caller id... all for under $200. Great deal if you ask me. Also, I'm sure you could find a better place to mount the control module, remember, you will still have one to place if you get the mobile-ease
Installation link:
http://www.fordfusionclub.com/index.php?topic=95937.0