Subscribing to Calendars
You can subscribe to calendars that use the CalDAV or iCalendar (.ics) formats. Many calendar-based services including Yahoo! and Google, and the Mac OS X iCal application support either format. Subscribed calendars are read only. You can read events from subscribed calendars on iPhone, but can’t edit them or create new events. You also can’t accept invitations from CalDAV accounts.