http://www.google.fr/m/url?client=safari&ei=zwM6TJDuH5WhjAfVzoGpAw&hl=fr&oe=UTF-8&q=http://www.iphonecoffee.com/tuto-downgrader-os-4-0-a-os-3-1-3-sur-iphone-3g.html&resnum=10&ved=0CCcQFjAJ&usg=AFQjCNH4RWqF10nUY1izJsml9Ap9PCSLIA
Je te conseille encore de ne pas downgrader 