As we just posted on UltraSn0w for iOS 4.2.1 is release for iPhone 3GS and 3G. But iPhone Dev Team has posted some long details with it on how to unlock iPhone 3GS and 3G on BaseBand 5.15 or 5.14. iPhone Dev Team said you will first upgrade to iPad Baseband 06.15 to be able to unlock your iPhone 3GS and 3G. This is the only option for all those who are on BaseBand 5.14 and 5.15 and want  to unlock. iPhone Dev Team has release new version of Pwnage tool 4.1.3 to actually jailbreak and upgrade the baseband of iPhone 3GS and 3G to iOS 6.15. This Guide is for Mac version. If you have an old-bootrom 3GS and are already unlockable but want to get to 4.2.1, please wait til iPhone Dev Team release an “unofficial” bundle for you.

Here is a full step by guide on how to upgrade baseband  6.15 on iPhone 3GS and 3G:

Step1: Download iPad iOS 3.2.2 from here.

Download Pwnage tool 4.1.3 here (bit torrent)

Download iPhone iOS here

Step2: Download iPhone and iPad iOS with Firefox not with Safari.

Step3: Launch Pwnage tool 4.1.3, press OK if prompt any warning. and Select Expert mode in top menu Bar.

Step4: a picture will be shown of iOS devices. select your respective device that is iPhone and click blue arrow button as shown below:

Step5: You will be prompted with “Browse for IPSW” page. browse your iPhone iOS which you downloaded earlier and click open. Pwnage tool 4.1.3 will give you warning on updating to Baseband 06.15. click yes if you are on baseband 5.14.02 or 5.15 and need an unlock, click no if you are on other firmware than 5.14.02 and 5.15.

Step6: Please read the following very carefully before deciding whether to do this.

1. There is no way to come back down from 06.15, and there’s no hiding the baseband version from Apple. You’ll be voiding your warranty in a very obvious way.
2. If some future baseband comes out with a critical fix, you won’t be able to update to it if it remains down in the 05.xx sequence (then again, you wouldn’t update to it if you wanted to keep your unlock anyway).
3. Starting with FW 4.2.1 if you have 06.15 on your iPhone you won’t ever be able to restore to stock firmware (it will fail). You’ll need to only restore to custom IPSWs (then again, if you’re unlocker you should already be doing that).

Don’t update to 06.15 if you don’t need to! Only do this if you need the unlock and you’re stuck on 05.14 or 05.15, and you’re willing to assume the above risks.

Step7: If you click yes so you will be prompted to browse for ”ipsw firmware” , browse for iPad 3.2.2 firmware and click blue arrow button.

Step8: You will be prompted with different options select build and click blue arrow button:

Step9: Now you will be prompted to save your iOS with baseband 6.15. after saving you will be giving a option a like shown below:

click NO in any case

Step10: Now you will be prompted to put your iPhone in DFU mode, simply follow those steps to put your iPhone in DFU mode.

• Press and hold the power and home buttons for 10 seconds.
• Then release the power button and continue holding the home button for 10 seconds.
• Once your iPhone is successfully in DFU mode, PwnageTool will prompt you to launch iTunes.

Step11: Once In iTunes, hold the Alt/Option key and click Restore. and browse for your cook custom firmware with baseband 6.15. and you are ready to go. wait for iTunes to install iOS on your iPhone.

Once you are done with custom iOS on iPhone. Now follow our guide here on how to unlock your iPhone  3GS / 3G on Ultrasn0w on baseband 06.15 here

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