In conjunction with Exchange Server 2003 Service Pack 2 (SP2) later this year this feature pack enables business users to easily stay connected to their Microsoft Office Outlook Mobile information while on the go and helps businesses to better protect device data.

• Keep your Calendar, Contacts, Tasks, and Inbox up-to-date using Direct Push Technology. Plus, you can now browse your corporate address book over-the-air with Exchange 2003 SP2.
• Better protect device data and manage devices using the Feature Pack and Exchange 2003 SP2. With this combination, IT administrators can remotely manage and enforce select corporate IT policies over-the-air via the Exchange 2003 SP2 console. Businesses can mandate policies like requiring PIN passwords for every device.
• Deploy scalable, cost-effective mobile messaging solutions and reduce the need to pay for an additional third party server product and client access license fees by using existing Exchange 2003 SP2 investments.

More details at http://www.microsoft.com/windowsmobile/business/5/default.mspx