Odd question --
We use a hosted Exchange solution that supports 8 iPhones and about 30 mailboxes for staff. On one iPhone, some appointments do not show up on the iPhone -- regardless of whether the appt was entered just by the user, appt created from a meeting request by another staffer on the same Exchange server, or appt created from a meeting request by someone external to the organization.
Not all appointments go missing from the iPhone, and all show up in Exchange/MSOutlook cached mode/Exchange WebAccess.
No pattern is evident in what appts go missing on the iPhone -- some are morning, some evening, some have lots of invitees, some have only the staffer in question and the meeting organizer.
In any interface where the appointment shows up, editing the details of the appointment -- even just adding a period at the end of the notes -- magically makes the missing appointment make the jump within 15 seconds to the iPhone in question.
System is hosted Exchange 2007, MSOutlook 2003 on the user's desktop, and iPhone 3G running 3.0.1 software.
I've searched online, the hosting company's knowledgebase, and apple support. The only close item is on corrupt appointment ... but a selective restore of past data on multiple occasions with different date ranges didn't fix the issue.