Adrian Beasley sent me this article the other day explaining how he managed to connect his Windows mobile 6 phone to connect to Exchange Server 2007.
It's certainly worth a read if you're struggling to get connectied and are running out of ideas...
Read it here...
Some extra resources that may also be of interest:
Configuring SSL and Exchange Active Sync
Active sync error messages when trying to sync a mobile device
Understanding Active Sync mailbox policies
Publish an Exchange server for OWA
Active Sync solution centre
Client side features in Outlook 2007