There will be a calendar in Fremantle
I think it wont use icalendar (at least as its main backend) because the new calendar API is really complete, with options for everything.

The S60 calendar has an important bug for me: if I delete a weekly meeting for just one day (and let the others untouched), from a random date every entry I had added is moved one hour early and it doesnt let me changed that. I had to buy Handy Calendar to use a calendar in the phone.