You're probably best off sending the VCAL object in a WAP push. (Where the WAP push points to a URL that contains the VCAL object.)
The WAP standards did define port 9205 (23F5 hex) for sending a vCal object (similar to how port 9204 is used for a vCard) without an external link. However, I don't know how widely this is supported (I haven't tried it myself).
The UDH would be 06050423F523F5.
The object encoding would be similar to how vCard is handled:
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