How To Update iPhone 4 on 4.2.1 Firmware using Custom Restore with 01.59.00 Baseband

These are the instructions on how to restore or update iPhone 4 on iOS 4.2.1 by preserving the baseband to 01.59.00 using Custom Firmware. Those of you who have already upgraded to 4.1 & 4.2.1 and are on their respective Modem Firmware (02.10.04, 03.10.01) this is strictly NOT for you. wait for the unlock to come.

Step 1:

Download the following files :

Custom Firmware of iOS 4.2.1 (iPhone 4)

Redsn0w 0.9.6b5 OR 0.9.6b6

Mac : Redsn0w 0.9.6b5
Windows : Redsn0w 0.9.6b5
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Mac : Redsn0w 0.9.6b6
Windows : Redsn0w 0.9.6b6

Stock/Original iOS 4.2.1 Firmware (iPhone 4)

Step 2:

Connect your phone with your computer and switch it off.

Step 3:

Open Redsn0w and browse original 4.2.1 firmware.

Step 4:

if your phone has new bootrom version then select Yes and click on the next button.

Step 5:

Select "Just Enter Pwned DFU Mode Right Now"

Step 6:

click on the next button and follow the on-screen instructions to put your device in DFU mode.

Step 7:

open iTunes. on Summary tab, hold shift key on your keyboard and click on the Restore button. A dialog box will appear , asking you to select .ipsw firmware. select custom 4.2.1 firmware and click Open.

Step 8:

wait for 5-10 minutes for phone to restore.

Step 9:

Disconnect your phone once the restore is complete and connect it again and launch Redsn0w.

Step 10:

Browse original firmware on Redsn0w & select "Yes" if your phone is a new bootrom model and click on next.

Step 11:

Select only "Install Cydia" as option and click on the next button.

Step 12:

follow the instructions and put your iPhone in DFU mode.

Step 13:

if your phone stucks, re-run Redsn0w and select only "just boot tether right now" option and click on next button.

Step 14:

Open Cydia and add repo666.ultrasn0w.com/ to install Ultrasn0w package so that you could unlock your phone.

You now have a fully jailbroken & unlocked iOS 4.2.1 on iPhone 4 with 01.59.00 baseband.