iTunes/iPhone syncing is done on a "per Mac" basis. In iTunes Preferences, go to Devices, and check the box for "Prevent iPods, iPhones, and iPads from syncing automatically". This will prevent iTunes from opening when a device is plugged in.
UPDATE: There used to be in previous versions of iTunes, in the old "Syncing" Preferences, a way to disable automatic syncing and that prevented iTunes from even opening. But it seems they have changed the behavior because searching for answers on other sites yield the same behavior but in previous versions of iTunes. I set this preference ages ago, so the preference must be holding over.
In response to your comments:
iTunes still starts, still does some
kind of mini-sync, but doesn't
recognise the name of the phone or
allow access to its contents.
Are you sure you are syncing with the iTunes install you originally started with? Syncing is strictly a one-to-one relationship for iPhones and iTunes. Once you sync an iPhone to an iTunes install and wish to sync with a different one (like on another Mac), you are then forced to clear the phone and start anew.
My iTunes behaves the way you are describing, but when I plug in my iPhone, I get the "mini-sync" you mention because that's the device registering with the OS and iTunes that it exists and iTunes puling needed info to interact with it. Can't really get around that one.
it would prevent the machine being
used at all for syncing, no?
No. You could still sync if you wanted, but that's if you are syncing with the iTunes install that recognizes the phone. Otherwise, see my comment above.
BTW, save the downvoting for the really egregious answers. Downvoting costs points. Otherwise, just leave it alone.
Note: This is all done on a Mac. Just look up the PC equivalent of the following steps if required.
How to recover past information:
Option 1 - Restore iPhone 4 directly from old computer:
- Connect iPhone 4 to old computer, open iTunes, put the iPhone in DFU mode, (while holding alt/option key) select Restore after iTunes has detected the iPhone 4 in recovery mode, and select the most recent backup of that iPhone 4.
Option 2 - Copy iPhone 4 backup from old computer, and place on new computer to recover:
On the old computer, go to ~/Library/Application Support/MobileSync/Backup, and copy the most recent backup of the iPhone 4 and transfer it to the new computer.
Connect iPhone 4 to old computer, open iTunes, put the iPhone in DFU mode, (while holding alt/option key) select Restore after iTunes has detected the iPhone 4 in recovery mode, and select the most recent backup of that iPhone 4.
How to create the ability to sync all purchased/future purchases of music and apps:
Open iTunes.
Sign out any pre-existing AppleID/iTunes Account once iTunes loads.
Sign into desired account of individual (your relative's I'm assuming).
In iTunes, select Store -> Authorize This Computer...
Rejoice!
Have your relative use iCloud for backup to make life easier in the future.
Let me know if you have any more questions, or need any futher explanation. Enjoy!
Best Answer
You're in troubles. :(
How you updated your iphone to IOS5-beta without iTunes 10.5? Asking because iTunes 10.5 is only for developers now.
from the: http://www.appleinsider.com/articles/11/06/06/apple_says_devices_updated_to_ios_5_beta_cant_be_restored_to_earlier_versions.html
In releasing several pieces of pre-release software -- iTunes 10.5, Apple TV 2 beta, Xcode 4.2 Preview and Lion Preview 4 -- to its developer community, Apple on Monday warned testers of its new iOS 5.0 software that any devices updated to the beta cannot be reverted or downgraded to previous versions.
You need iTunes 10.5 - developer release yet - whats mean register yourself as developer for 99USD/year.