Exchange calendar items not syncing

I'm seeing problems related to Exchange calendar items at one of my clients.

The first issue is that some calendar items, created either in Outlook or on an iPhone, appear on the creator's own Outlook calendar, but not on another user's computer on which the creator's mailbox is configured as an additional mailbox in Outlook.

The second issue is that some calendar items that are created on an iPhone appear neither on the creator's Outlook calendar, nor on any other user's instance of the creator's calendar.

They are running Exchange 2003, and a mix of Outlook 2007 and 2010.  The problem is independent of Outlook version.

I wonder if rights or flags are set differently on the iPhone-created events.  I'm not sure how to check this on individual items, other than to view them in Outlook.  Nothing stands out as being different when the items are viewed in Outlook, such as the private flag, which is not set.

There are no event log entries on the server that would indicate a problem, such as an ActiveSync error at the time when a calendar item is created on an iPhone.
Who is Participating?
Is this an issue with one user or all. If it's a single user problem then check the settings for Calendar on Iphone as per below article

There is a "known" problem with Exchange/ActiveSync Calendar sync and iPhone - which is due to timeouts more than anything. This may or may not be the cause of the problem you are facing, however, we have used the below patch effectively in the past to resolve similar issues to yours:
Sound like the issue may have a couple of cintributors here

One of the issues being known issues with Iphone and Missing calendar appointments

The second issue, being the possiblility of cached exchange mode being used

If cached exchange mode is being used, in conjunction with these devices, turn it off

This should help a bit more with the reliability
I would suggest first check how things look like if you check from OWA - Do you notice any difference.

If all looks good through OWA then moving Outlook to online mode and checking makes sense.
Also reconfiguring the profile on Iphone also should be tried.

First - What rights are given to the Second user on the First users calendar and is the Outlook profiles in cache mode ?

Second - Hope the correct Calendar is syncing with users iphone and hope both way sync is enabled ?

Did you check the IIS logs for Active sync logs ?

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