The default calendar is always the one in the default information store. If you set the profile so that mail is delivered to the Exchange mailbox, not the .pst file -- in other words, to the recommended configuration -- the mailbox Calendar folder will be the default.

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Sue Mosher, Outlook MVP
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> I've setup my outlook profile to connect to an exchange server and I've also
> created a pst file. With a client-side rule I automatically move all mail
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>
> Any help is welcome!