The exchange team announced beta 2 of Exchange Server 2007 SP1 with some interesting improvements for WIndows Mobiel device management

"Exchange ActiveSync Policies - New policies in SP1 build on Exchange Server 2007's security and management features with new policies for synchronization, authentication, and encryption.  For more advanced data protection needs, Exchange Server 2007 SP1 also offers device, network, and application controls.  These new features allow network administrators to help manage and secure Exchange ActiveSync enabled mobile devices"

Check the entire post on the Exchange blog at http://msexchangeteam.com/archive/2007/08/14/446656.aspx 

In another post on the same blog there are references to additional improvements beyond the policies including bandwidth optimization and S/MIME support (encrypted email).