C:\Documents and Settings\[username]\Application Data\Apple Computer\MobileSync\Backup\
On a Windows Vista or Windows 7 PC:
On a Mac Computer:
Note: To create a backup of your iPhone:
Your iDevices are backed up by iTunes each time you Sync with iTunes, update your device in iTune or Restore it in iTune.iTune usually backup all your data on the device such as Address Book, Applications, Messages, Songs, Videos, photos etc.
You can manually backup or restore your iPhone or iPod touch from a backup.To read about how to manually backup your iPhone, please read the first part of this article.