How to Jailbreak an unlocked iPhone 3Gs running on iOS4.

Recently my iTunes popped out a msg saying iOS4 is out for my iPhone
Excited(as always) I updated it thinking I could survive without my JB apps.
a day later I realized I did a major blunder.Because the dev-teamblog says

iPhone 3GS
Summary: Currently, PwnageTool only works on previously jailbroken 3GS devices with the old bootrom.

• If you have a Jailbroken iPhone 3GS with the OLD BOOTROM and you DID NOT use Spirit to jailbreak then you can create the ipsw with PwnageTool 4.0 and restore with your jailbroken recovery mode.  

• If you have an iPhone 3GS with the NEW BOOTROM this is NOT supported by PwnageTool 4.0 PwnageTool 4.01

I know I have an old bootrom because my s no. 3rd 4th and 5th nos. are 937 I think anything above 940 is the new bootrom. (CHECK)

BUT my device was not JB.  :((


(Before this process I remember clicking the "Make my life easier" button in Cydia.) when I was on 3.1.2. So this means I have the SHSH blobs or whatever it is on the Cydia server (YAY ! Cydia)

So I followed the steps here to downgrade my iPhone to 3.1.2
I got the 3.1.2 firmware from Google :D.

http://www.addictivetips.com/mobile/downgrade-iphone-3g-3gs-from-ios-4-to-3-1-2/

but towards the end I restored the phone in Recovery mode (press and hold the home button when phone is off and connect to your laptop) and not DFU mode(google DFU mode).
Try both.

It updated through the whole damn process and towards the end I got a lame iTunes error.
and my phone showed "Connect to iTunes screen"
So I fired up blackra1n (www.blackra1n.com) and within seconds my phone was jailbroken and running 3.1.2


NOW I HAVE AN OLD BOOTROM AND A JAILBROKEN iPHONE :D
I followed the steps posted on http://blog.iphone-dev.org/
So I created a custom firmware and Shift+Restored , when phone was in Recovery Mode.


Awesome BITE SMS here I come ;)



Hope this helps someone.Peace