Techworld reports on two options for Microsoft Exchange synchronization and support for the iPhone.
The two include, Visto and Synchronica. Due to Apple's reluctance to open the iPhone to 3rd party applications, both services provide different approaches:
Visto, for instance, which usually writes small handset-based applications to allow its email sync functions to work, will use a desktop PC-based application to forward corporate email to the iPhone
[Synchronica's] Mobile Gateway doesn't require system administrators to open ports in the firewall or install Exchange connectors. Instead it uses a separate server, located behind the firewall, that sucks in email via Outlook Web Access, already activated on many corporate email accounts.