A few people I know (not me personally, I don't currently own any Apple products) have had problems sync'ing their Outlook and iPhone calendars.  Below are the fixes that I've found have worked depending on the specific causes.  I suggest trying them in this order.

Fix 1:

1) Open iTunes
2) under "edit" open "preferences"
3) under the tab "Devices" click the button "reset sync history"
4) sync

Fix 2: Many people have reported better luck when their Outlook PST was in the newer Unicode Format.

Determine the format of your PST file: http://office.microsoft.com/en-us/out...

Convert your PST file: http://office.microsoft.com/en-us/out...

Fix 3:

Download the Microsoft Live Maps Add-in for Outlook via the following address:

http://www.microsoft.com/downloads/de...

Then once completely installed,  immediately go into Add/Remove Programs and remove it.  Attempt a re-sync with iTunes.

Fix 4:

Export your calendar into a comma separated values file and import into another calendar.  Sync to the new calendar.

If you know of, or find an additional possible fix, leave it in the comments.

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