While investigating why only some Outlook events showed up on a users iPhone calendar. I found that items created by the user or accept as meeting invitations were on both the iPhone and Outlook. But if it was created by another organizer, such as an assistant, on behalf of the user the event did not show on the iPhone calendar. [more]
The user was running an older firmware version 3.0.1, which was before the calendar invitation fix. I downloaded and installed the latest firmware version 3.1.2 and installed it on the iPhone. Once installed the iPhone resynchronized and all calendar events including those created by an organizer were present on the iPhone and Outlook.
So… installing firmware 3.1 or newer, breaks the free tethering option that can be installed on the iPhone. Not installing the latest firmware does not allow for the new calendar invitation options. Therefore a choice must be made.