Can I subscribe to a CalDAV or .ics calendar on the iPhone?
Yes, the iPhone supports subscriptions to both calendar formats. Several calendar-based services, such as Google, the Mac OS X iCal application, and Yahoo! support both formats. To subscribe to a calendar on the iPhone:
1. Navigate to Settings -> Mail, Contacts, Calendars -> Add Account
2. Select Other -> Add CalDAV Account or Add Subscribed Calendar
3. Enter your account information and touch Next
4. Touch Save
You can also subscribe to an iCal or other .ics calendar sent to your iPhone by touching a link to the calendar in the email or text message.