Yes I Can!

Jailbreak iOS 4.2 on iPhone 3GS with PwnageTool

iPhone 3GS ONLY, with older bootrom which has at least been jailbroken once with either redsn0w, PwnageTool, Blackra1n or Sn0wbreeze. If your phone is one of those with newer bootrom, and has only been jailbroken with Spirit or JailbreakMe, then this is not for you. You will end up getting 1600/1604 error when restoring the custom cooked firmware via iTunes. Also since Cydia is broken on iOS 4.2, make sure you install OpenSSH from here: http://apt.telesphoreo.org/cydia/debs/openssl_0.9.8k-9_iphoneos-arm.deb and here http://apt.telesphoreo.org/cydia/debs/openssh_5.2p1-8_iphoneos-arm.deb/ so that you can copy and install stuff without Cydia.

Step 1: Download PwnageTool 4.01

Step 2: Download the latest version of PwnageTool Bundle from msft.guy here and then extract it to your desktop.

Step 3: Download iOS 4.2 for iPhone 3GS, and iTunes 10 for Mac. You can get the official bits if you are a registered developer, or from different content sharing sites around the web. Please do not ask for the download links, a simple Google will do it all !

Step 4: Copy PwnageTool that you downloaded in Step 1 to your desktop. Right click, and then click on “Show Package Contents” as shown in the screenshot below.
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Step 5: Navigate to Contents/Resources/FirmwareBundles/ and paste iPhone2,1_4.2_8C5091e.bundle file in this location and then simply close this folder.

Step 6: Now start this patched version of PwnageTool, Select iPhone 3GS as your device and you will now notice that PwnageTool will automatically detect iOS 4.2 firmware file as shown in the screenshot below.

Step 7: Simply follow Step 5 to Step 7 posted to create a custom-cooked iOS 4.2 firmware file which will preserve your old baseband.

Step 8: You will now have to restore your iPhone to this custom firmware 4.2 file that you created using PwnageTool. Start iTunes, click on your phone icon from the sidebar in iTunes. Now press and hold left “alt” button (“Shift” button on Windows) on the keyboard and then click on “Restore” (Not “Update” or “Check for Update”) button in the iTunes and then release the “Shift” button.

This will make iTunes prompt you to select the location for your custom firmware 4.2 file. Select the required custom .ipsw file and click on “Open”.

Step 9: Now sit back and enjoy as iTunes does the rest for you. This will involve a series of automated steps. Be patient at this stage and don’t do anything silly. Just wait while iTunes installs the new firmware 4.2 on your iPhone. Your iPhone screen at this point will be showing a progress bar indicating installation progress. After the installation is done, iPhone will restart automatically and you should now have a fully jailbroken iPhone 3GS running on iOS 4.2.