A couple of months ago I wrote a simple script to grab a google calendar file and make it accessible by the ics file reader of your choice (orage in my case).
At work I got we have Sun Java systems communications express as a calendar and web mail system. Natively it doesn't recognise ics style appointments although it will import them.
Sun have this handy utility, csimport, to allow command line import of ics files so in principle you could add a line to the calget script something like:
ssh email@example.com csimport -c calid calendar calendarfile.ics
The only problem is that csimport needs to run as either root or the calendar server user which basically means a setuid type operation.
I've only started playing with csimport - it seems to overwrite duplicate events but I havn't done enough testing to be sure. If it doesn't nasty things with diff loom ...