CAUTION : iOS 4 jailbreak is way complicated unlike other jailbreaks. Please proceed with caution.
Requirements :

Jailbroken iPhone 3GS with older bootrom.
You haven’t used Spirit jailbreak before (for untethered jailbreak).
You have Windows (PC). For Mac, try Pwnage instead.
Please read the above requirements again.

More info about these custom firmware files :

[UPDATE] : You need to download files from either step 1a or 1b depending on your baseband preference. Both are unlockable, so I would go with step 1b which is the latest baseband which supposedly does better with the battery. step 1b …

Original iPhones (metal back, silver color, referred to as 2G iPhone) are blessed with a fully unlockable baseband 04.05.04_G. It entitles the iPhone 2G to be easily hackable. So lets get the ball rolling and get to the latest 3.1.3 firmware with a full unlock, jailbreak and activation in place!
Step by Step :
Download redsn0w 0.9.3 from downloads section and extract them to your Desktop [Both Mac and Windows versions of redsn0w are available there]
Connect your iPhone 2G to your PC/Mac and launch iTunes [Update iTunes to the latest version]

Update to …

CAUTION CAUTION CAUTION CAUTION : Please leave a comment if you don’t know what you are doing. Better safe than sorry. You are warned, now proceed!
iPhone 2G, 3G, 3GS users can now safely update to 3.1.3 firmware without updating the baseband (for unlock). If you are not the one to download all the various files and just want the ultimate result, these files are waiting for you to download! If you rather want to start from scratch, download Pwnage 3.1.5 tool for Mac.

Caution #1 : A restore is going to wipe the …

UPDATE : A new version of custom firmware 3.1 for iPhone 2G/3G/3GS is now available here!
Free your iPhone 3G 3.0 from Apple’s chain by jailbreaking your iPhone which provides you with various customization features and even unlock feature which Apple and your official carrier hate! There are various options available to achieve this level of customization on your iPhone such as download firmware files, bootloader files, jailbreak/unlock tools such as Redsn0w/Pwnage or QuickPwn.

If you are not the one to download all the various files and just want the ultimate result, …

Aviegas, a senior member at hackint0sh released ‘iPlus’ a much safer way to unlock your precious iPhone! The best part being the bootloader is now downgraded to 3.9 fakeblank BL which makes your iPhone brick-safe!! The best part being – it can now automatically install the all important applications :
– Installer
– Community Services
– BSD subsystem
– OpenSSH
– VT-100
Some Fixes:
– BSD Fix
– VT100 Fix
– Summerboard themes directory fix
– Relocates Fonts and Ringtones (More than 120MB free)
There is an option to upload packages to the iPhone during the unlock/jailbreak process in the …