Not Caldav. Old.
read this: Works ...(from prior post)
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Below is the response I got from Yahoo! Calendar Support.
Yahoo! Calendar Support essentially says iOS users should no longer use CalDAV account method but instead use the built in Yahoo! account option (Settings > Mail, Contacts, Calendars > Add Account > Yahoo!). Of course, this used to work for the calendar before iOS 5. Since then, all of us are trying the CalDAV option as an alternative.
Also, I noticed yesterday that Yahoo! updated the Yahoo! Calendar on the web. It has a nice look and feel in an attempt to better compete with the more robust Google Calendar. Perhaps, Yahoo! has been working hard at this and the integration with mobile devices has been on the back burner.
Suggestion to Yahoo! users on iOS 5 devices - Try using the aforementioned standard method for getting your calendar on your device. With the release of the new Yahoo! Calendar, maybe it's working now. Me? I gave up a few days ago. I'm now using Google Calendar.
Without further ado, here's the message from Yahoo! Calendar Support.
Thank you for writing to Yahoo! Calendar.
I understand you are experiencing sync issue with your Yahoo! Calendar using your iPhone device. I apologize for the inconvenience this has caused you. Let me address your concern.
If you recently upgraded the operating system on your iDevice (iPhone, iPad, iPod Touch) such as with the recent release of iOS 5 software for Apple iDevices that could be the cause of the syncing issues.
You can delete the Yahoo! account from your Apple iDevice and recreate it, forcing a new sync, which should bring all your information over from Yahoo! Calendar.
Please note that CalDAV accounts are no longer needed on your iDevice to sync with Yahoo! Calendar and you may delete the CalDAV account if you have it set up on your iDevice. If you have a CalDAV account set up and do not delete it from your iDevice, you risk getting duplicate calendar layers & events on your iDevice and in Yahoo! Calendar.
To remove your Yahoo! Calendar CalDAV account from your iDevice:
- Go to your iPhone, iPad, or iPod Touch "Settings" application.
- Tap "Mail, Contacts, Calendars."
- Tap "Yahoo! - Calendars, Reminders."
- Tap "Delete Account", Confirm deletion by tapping "Delete Account" once again.
How to sync your Yahoo! Calendar and Yahoo! Address Book with your iDevice (iPhone, iPod Touch, iPad)
- Go to your iDevice's "Settings" application.
- Tap "Mail, Contacts, Calendars"
- Tap "Add Account" and then tap "Yahoo!". You may already have a "Yahoo!" Mail, Contacts, Reminders, and Notes account set up; if so just tap it under the accounts section.
- Enter your Name, Yahoo! E-Mail address & Password. You do not need to change anything in the "Description" field unless you wish to. Tap the "Next" button, upper right hand corner, when you have entered the information and Yahoo! will verify your account information.
- Click the "Save" button in the upper right hand corner
- Still in the settings for "Mail, Contacts, Calendars", set the "Fetch New Data" to every 15 minutes or whatever time increment you desire, you may leave the "Push" setting on or turn it off, it is not relevant to Yahoo!'s services.
- To ensure proper syncing between your iDevice's Calendar and Yahoo! Calendar, please make sure the "Default Account" account is set to one of your Yahoo! Calendar Layers from Yahoo! Calendar in "Calendars" found towards the bottom of the settings for "Mail, Contacts, and Calendars". It defaults to iCloud and if not changed to one of your calendar layers from Yahoo! Calendar, syncing will not work.
- You can come back to Yahoo! Mail, Contacts, Reminders, Notes to disable syncing for all or specific Yahoo! Services or to delete your Yahoo! Account from your Apple iDevice.
I hope the information provided has been helpful. Please don't hesitate to reply if we can be of further assistance.
Thank you again for contacting Yahoo! Calendar.
Regards,
Flora
Yahoo! Calendar Customer Care