Yahoo Calendar - CalDAV
If you are running iPhone 3.0 software (released Summer of 2009) or newer, syncing calendar to your iPhone can be done without plugging into your computer.
Make sure you are using the Calendar Beta. If you go to calendar.yahoo.com do you see the words “Yahoo! Calendar Beta” in the top left corner? If you are not using the beta you can switch to it by visiting switch.calendar.yahoo.com
Go to your iPhone settings application.
Tap "Mail, Contacts, Calendars".
Tap "Add Account".
Tap "Other" and then tap "Add CalDAV Account".
For the "Server" you can simply type "yahoo"
Now type in the Yahoo! username and password you use to signin to your calendar
Once you click save, the iPhone will verify your username and password.
Next time you open up your iPhone Calendar you will see a page allowing you to select with Yahoo! Calendar layer you want to view/edit.
It may take a few minutes for your Yahoo Calendar info to load... be patient.
PC, Windows XP