Recently a user synced his iphone to an SBS 2003 box , however email would only come through when their Outlook was open recieving mail , or the user would read the email in Web Access. This is an issue to do with Active sync and Trend Antivirus that the below registry entry fixes :

Browse to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\MSExchangeIS\VirusScan via regedit

Change the value of “ProactiveScanning” to 1 and close.

Restart IIS and Exchange services to make sure it gets applied.