It appears that anything I am invited to with multiple attendees does not show up on my iphone. I thought it's iphone issue with Exchange ActiveSync at first place, but I found out the events are not in OWA either.
I followed these two KB articles below to resolve the issues in my environment. (Exchange 2003 SP2 & Outlook 2007)
Requested and installed the hotfix in KB938650 Clicked on "Fix if for me" to create the registry in the same KB938650 Created "CalendarRecovery" reg key in KB969254 Changed Outlook profile to 'non-cached' mode Added "CleanupExpansionCachesInTheCalendarFolder" in description of Outlook Calendar
The past missing events show up both in OWA and iphone4s