My Iphone 3GS 3.1.3 ----> 4.0.1 HELP!!!

hello..

i have a problem on my iphone 3gs which is in 3.1.3 and i want to update it in OS 4.0.1
is it possible?

i tried f0recast and this is the result...

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Serial # :
Baseband : 05.12.01
boatloader : 6.4
Model : MC137
-----
Jailbreakable? : Only if SHSH is saved
Unlockabled? : NO
Tethered? : MAYBE - depends if refurbish...
-------------------------------------------------------

I need your help to decide things up, because i want to upgrade my iOS to version 4.0.1 and im affaid that maybe it will be not unlocked after performing this task..??   
i dont want my phone to become useless because its my only phone..



NOTE: im using Windows Machine.. and if i perform this task i want it to be activated already because i dont have a AT&T sim to activate the phone..



THANK YOU..
IPHONE3GS.ORG RULEZ    

i know it can be activate.. like b4 im using snowbreeze or redsnow to activate and jailbreak iphone.....

Im planing to upgrade my iphone 3gS to 4.0.1 to have multi tasking, etc,, specialy run apps that are for OS 4 only.. and its a must for me....


@Pizentu
read on redmonpie post.. iOS 4.0.2 can be jailbroken with redsnow.. for your info if you dont know..

http://www.redmondpie.com/jailbreak-ios-4.0.2-with-redsn0w-how-to-guide/





PLs.. need help for my problem because still i cant sloved it..