Yes, Google CAlendars.
I don't follow you though. In the instructions I listed above, there is no instruction to select "Add Calendar".
I have the multiple calendars for ONE login. So I manager calendars once logged in, and added my Work calendar.
For my wife's calendar, we just turned on sharing of her calendar with mine and it is on the list of calendars to replicate.
If you are wanting to bring down a different calendar with a different login, then you need to go into the calendar program; select Menu, CAlendar Sync, then on that screen at teh bottom will be a button "Add Accounts". I didn't want to use that for my wife's because then when I go to the sync settins, I have 2 optoins: Sync Contacts, and Sync Gmail. I don't want to sync her mail, or contacts, just the calendar.