Apple iOS 4.0.1 fixes Exchange ActiveSync issue
Image courtesy Engadget:

The iOS 4 issue wit Exchange ActiveSync (EAS) which resulted in iPhone 4 and other iOS devices running the OS not being able to sync with Exchange Server (see Apple fixes issue with iOS 4 and Exchange ActiveSync), has been fixed in iOS 4.0.1. Earlier Apple released a configuration profile to change the device timeout to 240 seconds. iOS 4.0.1 includes the configuration change.

http://exchangepedia.com/2010/07/ios-4-0-1-includes-exchange-activesync-fix.html