Two-way mobile Exchange connectivity currently comes in three general flavors -- PDA synchronization, Wireless Application Protocol (WAP) devices, and BlackBerry/2-way pager devices. In all cases, a server or wireless service (or both) is used as an interface between the Exchange Server and the mobile device.
Other mobile access tools can be found on the following pages:
This page lists server-based solutions that connect directly to Microsoft Exchange. Standalone, mostly non-Exchange users can get two-way mobile access with these tools and services listed at Tools for Mobile Access to Microsoft Outlook Data.
For developers: RIM and BlackBerry Developer Resources