Some iPhone users do not know that upgrading iPhone to the latest IOS will also update the baseband. If you would want to use other carriers, then you have to undergo the process of unlocking your iPhone. Nowadays, the most popular unlocking tool is the UltraSn0w, however, it does not support new baseband versions. Thus, for iPhone 4 users who want to upgrade to iOS 4.1, you have to take extra step to preserve the supported baseband, i.e. 01.59.00. Upgrading to the latest version (2.10.4) will make your iPhone unlockable.
Now, follow these steps to upgrade to iOS 4.1 without updating to the latest baseband version.
Step 1: Download TinyUmbrella
Step 2: Run TinyUmbrella
Launch this little program to start the process. Make sure you have switched off your firewall or allow your firewall to run this application. It is advisable that you run it as administrator if you are using Win Vista or Win 7.
Step 3: Connect iPhone
Make sure your iPhone is connected to your computer and that TinyUmbrella has detected it and its firmware.
You can click on ‘Save My SHSH‘ button to save a backup of your SHSH blobs should you need to downgrade your iPhone in the future.
Step 4: Start TSS Server
You may now click on ‘Start TSS Server‘ button so that TinyUmbrella can start killing iTunes. By doing so, you will be able to see ‘Running’ status just below the button.
Step 5: Launch iTunes
While TSS server is running, launch iTunes to restore iOS 4.1 firmware.
Step 6: Restore Firmware
Select your iPhone among the list of devices in iTunes. Press and hold the ‘Shift‘ key then click on the ‘Restore‘ button. This will let you navigate through the directory where you have download the iO 4.1 firmware a while ago. Be sure to look for iPhone3,1_4.1_8B117_Restore.ipsw.
Step 7: iTunes Error Prompt
Sit back and wait for the process to be done. An iTunes error 1004 will be your sign that the whole process is complete. This error simply means that your iPhone is running iOS 4.1 and has preserved its baseband version. Thus, you can use UltraSn0w to unlock it and use other carriers.
Step 8: Kick Device Out of Recovery Mode
Now, go back to TinyUmbrella and click on the ‘Kick Device Out of Recovery‘ button to conclude this process. But make sure you still have your device connected to your computer. By clicking that button, your iPhone will automatically reboot.
After the reboot, your iPhone should be running iOS 4.1 with the same baseband version, 01.59.00.
This month, there are two jailbreaking tools released for jailbreakers – limera1n and greenpois0n. Having this baseband version, you can use limera1n to jailbreak your iPhone and use UltraSn0w to unlock it.