So I have a 3GS. It's host iTunes computer died and there are no backups. I wanted to get it synced up again without losing anything so I attached it to a new Mac. Every step along the way it threatened to wipe everything out if I synced. I logged into iTunes store using the same account the other one was, then I did transfer purchases. This got the songs and apps into iTunes. So far so good. Then I went into syncing options for calendars and contacts and they got imported into iCal and Address Book. Syncing stopped threatening to delete everything, and everything *seems* ok. Now here's my problem - I want to upgrade to iOS 4. But when trying to do this, I get more scary messages about it wiping out my phone. At no point during this processes did I ever become confident that this iPhone really "belongs" to this Mac's iTunes. I am worried that it is more of a guest. Even though I have all my songs and apps, I don't know what the state of all my application data will be - all those stored passwords, game progress, weight loss logs - I have no idea if those things are going to just disappear after I upgrade. I haven't been able to find an answer to this question - not one that addresses the safety of my app data. Anyone know?