I finally resolved (well, circumvented would be a better word) my problem with iPhone-Outlook calendar synchronization by switching to use an Exchange server for my calendar. There was one more gotcha, though. I found that events I added to the calendar on Exchange were appearing on the phone as invitations. This is bad because, for example, you can’t edit those events. A similar issue happens with events you create on the iPhone and then edit on Exchange.
It turns out that the iPhone uses the email address of the event originator to distinguish between appointments and invitations. If the email address you use when configuring the phone doesn’t match the email address verbatim (i.e., case-sensitively and ignoring aliases), you get this behavior.
More at Apple support article TS1865.
Internet Scofflaw 