iPhone 3g's firmware 4.0.2 -> Downgrade to 4.0.1 and unlock

Since apple has stopped signing 4.0.1 and 3.2.1 SHSH requests for all devices now. If you missed your chance - I'm sorry. There's nothing that can be done now. If you had a 'Pending TSS Request' and DID NOT use TinyUmbrella to save your SHSH then I'm afraid you may not have your SHSH's saved on Cydia. If you DID use TinyUmbrella to save your SHSH then it's guaranteed that Cydia has your SHSh and is just processing them locally before they show up on your Cydia Home Page. For further information, please follow this link.
IF YOU HAVE NOT SAVE YOUR SHSH,
Follow this step's.
1 - I downloaded TinyUmbrella for win @ for osx.
2- Run TinyUmbrella. Click Advanced Option. Select 3Gs 4.01. Select Cydia. Save SHSH.

It will give a message say " Successful SAVED " something like this from memory.

With BOTH Already saved or JUST SAVED USE THIS STEP TO RESTORE BACK TO iOS 4.01
3 - Start TinyTSS Server, Same steps as above but Select 3Gs 4.0.2 (cant be too safe)
4 - Edited Local host to say following: 74.208.105.171 gs.apple.com
5 - Rebooted iPhone into Recovery Mode, chose 4.0.1 IPSW
and after restore to lower fw, just jailbreak using www.jailbreakme.com and inject ultrasnow
viola thats all.

ps: You must have this JAVA application Install to be able to use Tiny Umbrella
special thanks to MPhoneClinic.