I don't know if I know the correct answer, but from my research (as I am kind of in the same boat) this is what I have found. You will be able to connect to Exchange 2007/2003, but it might take some monkeying (allowing connect without a password for specific users) and downloading an app or two, but you will be able to do it...
That being said, I don't know if you will be able to do it without this process and simply using your standard SSL setup. I hope so and will be messing with that when I get it, but, as for being certain in an answer, all I can say is that you will be able to connect in one way or another.
For reference, here is one of the apps that I've seen get props:
Exchange by TOUCHDOWN
Anyone else have more of a definite/detailed answer?