Windows:
http://www.iphoneitalia.com/guida-effettuare-il-jailbreak-per-iphone-3gs-win-43305.html
Mac:
http://www.iphoneitalia.com/guida-effettuare-il-jailbreak-su-iphone-3gs-con-purplera1nmac-43870.html
Mac, Windows, Linux:
http://www.iphoneitalia.com/guida-redsn0w-0-8-come-effettuare-il-jailbreak-su-iphone-3gs-44325.html