My iPhone was a locked one with 3.1.3 upgrade. I jailbroke it using redsn0w-0.9.4(windows). There is a trick at this step while start cracking firmware 3.1.3, you need to point 3.1.2(iPhone1,2_3.1.2_7D11_Restore.ipsw) firmware path to break 3.1.3(iPhone1,2_3.1.3_7E18_Restore.ipsw) while selecting firmware on first screen of redsn0w. This works just perfectly.
STEP 1: Jailbreak your iPhone 3.1.3 using redsn0w, and make sure you select ‘Cydia‘ it needs to be therein for installing some utilities to determine, upgrade/downgrade and unlock purposes later.
STEP 2: Install Cydia/Terminal in your iPhone and check version of your baseband firmware, you need to use BBUpdateExtreme for this. It is a bit techie but prefect utility for checking baseband version, it showed different but correct info to me than other options I tried. It involves quite a long procedure so please refer to iPhoneHeat for this. You are lucky if it shows ICE2_BOOT_05.08_G2M3B2 to you, as it’ll increase your chances for unlocking your iPhone 3G to almost sure.
STEP 3: Now go to Cydia on your iPhone and Search for Fuzzyband and then install this application. Start fuzzyband and hit downgrade button to make your bootloader compatible for unlock/ultrasn0w. You are lucky if you see successfully downgraded message.
STEP 4: Almost done, now quickly install ultrasn0w and run it……………………DONE!Get to know the crack as soon as my friend posts it!
Please read the complete post on