I have a friend who had their G5 die, and they are relying on their iPhone while waiting for their new iMac to ship. However, they have been having issues with the various bugs in the iPhone's 2.0.x software. So I decided to update their iPhone from my MacBook Pro. I couldn't find any documentation that said if it was possible, so I gave it a try. When you first plug in the other iPhone, iTunes asks you to erase and sync the phone; hit Cancel at this point. Next, select the iPhone in the Devices column, and uncheck the 'Automatically sync when this iPhone is connected' and 'Sync only checked songs and videos' boxes in the Options section of the Summary tab. Now click the Update button to run the update. The iphone will do its update thing, and no data will be lost. ...
Anytime
