I finally pieced together how to get Yahoo calendar details synched to the Iphone. Note that this is a one way data transfer, from Yahoo to the Iphone. I am posting this because every other forum said it could not be done unless you use a solution like Plaxo. The process is really pretty simple: No Need for Plaxo or anyother third party. Important: Download the latest beta version of Yahoo Calendar (Link Below) http://switch.calendar.yahoo.com/m/landing.php Once you have this Set-up you can go to Ical and follow these instructions from Yahoo: In the iCal menu, select Preferences. Click on Accounts. Click the "+" sign in the bottom left to set up a new account. If your email address ends with @yahoo.com, use this URL: https://caldav.calendar.yahoo.com If your email address does not end with @yahoo.com (i.e. @ymail.com or @yahoo.fr) use the following URL instead: https://caldav.calendar.yahoo.com/principals/users/your_username@your_domain/ If your email address ends with @yahoo.com, enter your username without the @yahoo.com at the end. If your email address does not end with @yahoo.com (i.e. @ymail.com or @yahoo.fr), you will need to include your full email address as your username. OK, great. Your password is the same one you use to login to Yahoo! products such as Calendar and Mail. After this is complete, you will be able to update your yahoo calendar and then the information will be transferred to ICal. From ICal you can update the iphone using itunes. The last two steps are documented in detail so I am not going into details here. I am also sending this to apple support since they were unable to get this working but interested in the solution if I found one.