Backups can be created in the following ways:
Once iPhone has been configured to sync with a particular computer, iTunes automatically makes a backup of iPhone on that computer when you sync. iTunes won’t automatically back up an iPhone that isn’t configured to sync with that computer. If you’ve configured iPhone to automatically sync with iTunes on a specific computer, iTunes will back up iPhone every time you connect it to that computer. Automatic syncing is turned on by default. iTunes only makes one backup each time you connect, even if you sync multiple times before disconnecting.
If you choose to update the software on iPhone, iTunes will back up iPhone automatically, even if it isn’t configured to sync with iTunes on that computer.
If you choose to restore the software on iPhone, iTunes asks if you want to back up iPhone before restoring.
If you use a Bluetooth headset or car kit with iPhone and you restore settings, you must pair the Bluetooth device with iPhone again to use it.
For more information about backups, including the settings and information stored in a backup, go to www.apple.com/support and search for HT1766.