Not sure about GM, but I managed to upgrade iOS 5.1.1 on my 4S to iOS 6 Beta 4 without losing much. Instead of Restore, I held shift and clicked on Update instead, then chose IPSW file for B4. The only hick-up was that I have iTunes Match, and during the update the setting got toggled to OFF (all my music was still on the phone though). Obviously, when I toggled it back on, it deleted all my music and I had to re-download whatever I physically wanted on the phone from iCloud. Other than that, all apps (along with settings and saved data), videos, settings, call/text history, etc. were preserved.
Correct. Although if you are planning to install iOS 6 GM before it is released to general public, you will need to perform "wired" upgrade, in other words, get your hands on IPSW file and connect your iDevice to a computer to do it. I seriously doubt Apple will make OTA upgrade available before the official release date. Well, maybe they will offer OTA GM upgrade to Beta users; however, those running 5.x will have to wait until it is officially out.
if you have beta 4 installed and click check for updates it will just say your up to date you would need to either downgrade or dfu or recovery mode the device hit restore and let it download iOS 6
or ignore what I said lol backup the phone and hit restore and it will download iOS 6 and restore to official build and restore from backup
