do you want jailbreak and unlock your iphone 3Gs 3.1.3? may be yes, so redsn0w do this for you.
in this video i am gonna to show you how to jailbreak and unlock iphone 3gs 3.1.3
YouTube - how to unlock iPhone 3G/3GS 4.0/3.1.3
YouTube - how to jailbreak iphone 3G/ipod touch 2G 4.0 ( multitsking and wallpaper for iphone 3G/ipod 2G)