Unlike other cell phones and PDAs, all of which use your computer's mobile sync utility, iPhones are backed up through Apple's iTunes. Even though backing up your iPhone with iTunes is very simple, the procedure is not readily apparent in iTunes. Restoring your iPhone to the most recent backup is also easy. Whether you use a Mac or a Windows machine, backing up and restoring your iPhone is the same on either platform.
Backing Up Your iPhone
Make sure your iPhone is turned on and functioning. Plug the iPhone-compatible USB cable into a USB port on your computer, and then plug the cable into your iPhone. Your computer will recognize the iPhone, install the necessary drivers and start iTunes. (If this is the first time you have connected your iPhone to this computer, iTunes will check your phone to make sure that its software and firmware are up to date. If either is not, you'll be prompted to update the phone. You should choose "Yes." The update process takes several minutes. When it's finished, the iPhone reboots and the phone is displayed under the "Devices" section in the left column of the iTunes interface.)
Click your iPhone in the "Devices" section of the left column of iTunes. This displays a screen with information about the phone, such as the phone's name, storage capacity, serial number and so on. You can also use this section to sync your phone with your computer, which is slightly different from backing up the device. iTunes will automatically sync your phone with your computer each time you connect the two devices.
Right-click your iPhone in the "Devices" section of iTunes and choose "Backup" from the fly-out menu. Your iPhone is now backed up to your computer.
Restoring Your iPhone
Make sure your iPhone is turned on and functioning. Plug the iPhone-compatible USB cable into a USB port on your computer, and then plug the cable into your iPhone. Your computer will recognize the iPhone and start iTunes
Click your iPhone in the "Devices" section of the left column of iTunes. This displays a screen with the aforementioned information about the phone.
Click the "Summary" tab, and then click "Restore. iTunes prompts you to back up your phone. Unless you have just backed it up, you should choose "Back Up." iTunes prompts you again, asking if you want to restore the phone. Click "Restore." When the restoration completes, click "OK." iTunes displays the "Set Up Your iPhone" dialog box.
Click "Restore from the backup of..." . Then, click the drop-down menu and choose the iPhone backup set you want to restore to your phone. The backups are listed on the menu by date. Say, for example, you're restoring your phone because it stopped functioning properly. In this case, you would choose the backup on the latest date before the phone started acting up.
You can also use iTunes to transfer the configuration of one iPhone to another. Simply choose the “Set Up as a New iPhone” option in the "Set Up Your iPhone" dialog box.
During the restoration process, the iPhone is returned to the factory settings. Make sure your computer is connected to the Internet before you start restoring the phone, so that your iPhone can be reactivated.