Issues with iPhone4/iOS4 and ActiveSync with Exchange Online

The MS Online Team blog has an article about what you need to do if you are running an iPhone4 or iOS4 and are having difficulties with synchronising to Exchange Online:
I am running an iPhone 3GS with iOS4 and not experiencing this issue, however have seen it written about on several forum and blog sites.
Hopefully if you are feeling the pain this will fix it for you.