on 10-07-2015 12:12
Just so those interested are aware the public beta for iOS 9 was deployed yeterday. Users can sign up at beta.apple.com.
You need to install a profile on your phone and the update is downloaded OTA
Ensure you make a full backup to iTunes before installing the update just in case.
This is the same version as those in the developer program, includes Apple Music and the new News app (though this is prone to crashing from reviews available at the moment).
on 10-07-2015 12:47
The iTunes back ups are working, from what I understand is people are upgrading then deciding on a full restore at which point the original backup cannot be used as it comes from an earlier version of iOS, the backup created will only work with the iOS version installed on the users phone when competing the backup.
There are ways to revert back to iOS 8.4 at the moment anyway (though not earlier as Apple have stopped signing 8.3).
If you do this and are considering a restore for a fresh phone afterwards it is recommended to run another backup after the installation of 9 so that the backup can be used with 9.