If your iPhone crashes and erases your saved contacts and phone settings, don't despair. Use the option to restore your data that iTunes offers, provided you have a backup available. Restoring contacts from a previous backup created in iTunes saves you the time and effort involved in retyping each contact lost from your iPhone.
Download and install the latest version of iTunes if you do not already have it on your computer (full link in Resources).
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Connect your iPhone to the computer using the supplied USB cable; if you have a Wi-Fi connection, your iPhone does not require a connection. Launch iTunes if it does not launch automatically. Click the "iPhone" button.
Select "Restore" from Summary tab.
Decline the option to make a backup if prompted by selecting "Don't Back Up."
Select "Restore" to confirm you wish to restore your iPhone. Your last backup, including contacts, restores to your iPhone. Your iPhone will re-start and display the Apple logo.
Follow the steps offered by the iOS Setup Assistance for iOS 5 and later to clear the "Connect to iTunes" message. For earlier versions, leave your iPhone connected via your USB or Wi-Fi until the message "iPhone is activated" appears.
Apple recommends that you back up your iPhone, especially before any kind of servicing or repair.