This is a bit of a long shot but I have Exchange 2003 running on W2000 (I know, not supported, but it is a very small setup)
My Windows Phone 7.8 works fine but I cannot get the iPhone to sync using Active Sync. I do not have an X509 cert installed on this setup. Could this be the reason the iPhone does not connect even though I have unticked the use SSL box on the iPhone. The Windows Phone does connect when the SSL box is unticked.
The iPhone is up to date and a 4S.