Does your phone sync during an iOS upgrade? If so, what does it sync and can you "not" sync it by having the items unchecked?
Does it make a difference if you have iTunes set to not sync automatically when connected (under preferences)?
iTunes doesn't really sync a thing onto the iPhone during iOS upgrade. What the recent version of iTunes does during iOS upgrade is that it makes sure that everything are back onto your iPhone after the upgrade so you waist no time trying to sync everything back to the iPhone after the upgrade.
1.) iTunes make sure that the iPhone is authorized to sync with the iTunes.
2.) iTunes make sure that all apps on the iPhone are present on the iTunes, if that's not the case, iTunes adjust by auto syncing up apps so that only apps present in the iPhone are present/ checked in iTunes.
3.) iTunes makes sure that musics present in the iPhone are also present in the iTunes music library and are checked.
4.) iTunes save a copy of your iphone settings, contacts, SMS in a small backup file.
These process taking place at the beginning of the installation of the very new IPSW, you will see "preparing iPhone to restore" or something like that at the beginning of the installation.
When the installation of the IPSW is done, you iPhone will reboot, iTunes will notify you to not disconnect the iPhone until it finish rebooting, after the reboot of the iPhone, iTunes will now automatically restore back into the iPhone those apps, songs, contacts, settings etc... usually iTunes takes less time to load back those info into the iPhone than when doing a backup restore. When that's done you will be ready to go and your iPhone will be the exact same thing minuts before the upgrade except for the new iOS version and all it's new features.
Basically, you don't need to sync a thing when upgrading iOS.
But even though the recent iTunes are set to work like that with iOS upgrade, it's highly adviced to do a backup of the iPhone before doing a software upgrade, iTunes is just a software and can crash when not expected.
