This post will show you how to Jailbreak, flash iPad 06.15.00 baseband and Unlock iPhone 3GS on iOS 4.2.1.
1. Redsn0w Download.
2. Download your custom IPSW firmware for your iDevice here.
3. Right click Redsn0w and set compatibility to windows XP (service pack 2) if you are on Windows 7 or Windows Vista and run as administrator.
4. Connect your iDevice to the Computer and turn it off; after you have done this run Redsn0w (If it isn’t already connected).
5. Make sure your firmware is somewhere you will have no trouble finding it, preferably your desktop. Browse for your 4.2.1 firmware in Redsn0w and select it.
6. Click next and then check install Cydia (if it is already checked then leave it) AND “Install iPad Baseband”.
7. Click next and follow the on screen instructions to put you device in DFU mode. The steps are as follows:
I. Hold down the power button for 3 seconds
II. Continue holding the power button and start holding the home button and continue HOLDING BOTH for 10 seconds
III. Let go of power and continue holding home button for 20 seconds (or until Redsn0w starts the jailbreaking process).
8. Wait for it to finish.
9. When it boots up launch Cydia Select User and Refresh your Cydia.
10. After it refreshes, search for ultrasn0w, install it and reboot your iDevice.
11. That’s it put in your sim card and give it about 2-3 minutes to catch signal.
9.You are now jailbroken and unlocked, may the jailbreak and unlocked forces be with you!