Snowbreeze v1.5 has been released which can jailbreak iPhone 2G, 3G, 3GS (Old Bootroms only) on iPhone 3.1.3 firmware.
You can follow our guide on how you can jailbreak iPhone 3G, 3GS on OS 3.1.3 using sn0wbreeze.
Snowbreeze preserves your baseband while upgrading you to the lastest iPhone OS 3.1.3.
Which enables you to unlock your iPhone 3G, 3GS using the current version of ultra sn0w for baseband 04.26.08 or blacksn0w for 05.11.07 as both are compatible to work with older basebands.
Follow the instructions below to unlock iPhone 3G, 3GS on firmware 3.1.3 using ultrasn0w. iPhone 2G users can follow redsn0w 0.9.4 guide to jailbreak and unlock their iPhones.
Once your iPhone is jailbroken, start “Cydia”, and touch “Manage” tab on the bottom. Now touch on “Sources”.
Note: T-Mobile users should disable 3G before installing Ultrasn0w.
Touch on “Edit” then on “Add” and you will be prompted to add a url source. Type “http://repo666.ultrasn0w.com” and touch on “Add Source”.
Now Cydia will automatically update your sources following a series of automated steps.
Once it has been added successfully, search for Ultrasn0w in Cydia and install this application. Latest 0.92 version of this application will automatically unlock your iPhone so that you can use your iPhone with any carrier with proper carrier name/logo.
Now simply restart your iPhone, and you will have an unlocked iPhone 3G/3GS on iPhone firmware 3.1.3.