Update: Apple had stopped signing iOS 4.3.5 on October 17, 2011 so this guide is NOT valid. However some people claim that they can downgrade with chip replacement. However chip replacement is so risky for your phone that you should only look around your local store with this service.
If you already upgrade your iPhone iOS to iOS 5.0 or 5.0.1 with iTunes, you might notice that your current baseband is 4.11.08. Currently this baseband can’t be unlocked. However with this article, I will give your instruction to downgrade your baseband from 4.11.08 to 4.10.01 so you can still unlock your iPhone while enjoying iOS 5.0.1.
- Download iTunes 10.5
- Download iTunes 10.4.1
- Download iOS 5 or 5.0.1 for iPhone 4
- Download iOS 4.3.5 for iPhone 4
- Download TinyUmbrella
- Download Redsn0w 0.9.10 b3 for here (For Windows, you must be in administrator mode to run RedSn0w)
Guide to Downgrade Baseband 4.11.08 to 4.10.01 to Unlock iPhone 4 on iOS 5.0.1
Step 1: Check out the version of your current iTunes, if it is on 10.5, you need to downgrade to 10.4.1. Click here to find instruction to downgrade iTunes 10.5 to 10.4.1.
Step 2: Start iTunes 10.4.1 and click on iPhone 4 icon and select “Restore” so you can point to the iOS 4.3.5 (downloaded above).
Step 3: Wait for iTunes to set your device back to iOS 4.3.5. After completing, you can insert the official SIM card (the one you bought with the phone). If you accidentally lose it, you can use TinyUmbrella to confirm your baseband is 10.4.1.
Step 4: Build custom iOS 5.0.1 for your iPhone 4 with 0.9.10 b3. Here is guide to upgrade to iOS 5.0.1 preserving current baseband.
Step 5: After the custom iOS 5.0.1 was build, you can install iTunes 10.5 again and start the new iTunes.
Step 6: Now you will have to set you phone into DFU mode. Follow the below steps:
- Press and Hold Power and Home Button for 10 seconds. Now you can release the Power button while keep holding Home button for another 10 second.
- Now you are in DFU mode.
Step 7: Use iTunes to restore your iPhone 4 with the iOS 5.0.1. Start iTunes 10.5 and click on iPhone 4 icon and select “Restore” and point to the new custom iOS 5.0.1.
DONE! Now you have your iPhone 4 running on iOS 5.0.1 with 10.4.1 that you can unlock with Gavey SIM.
How to Use Gevey SIM on iPhone 4:
Step 1: Make sure that your SIM were cut to fit with the smaller size Gevey SIM.
Step 2: Insert the new SIM with Gevey SIM and turn on your iPhone 4 and click on “Accept”.
Step 3: Count to 15 second after clicking “Accept” and then call 122 and hang up just after 2 seconds.
Step 4: Go to phone Setting and turn on “Airplane Mode” and turn it off. You will receive “SIM failure” message.
Step 5: Now turn the “Airplane Mode” and turn it off. You will receive “SIM failure” message. Wait a few second that you can see the signal starts to show up.
You might repeat the steps if your Gevey SIM is not working. You should understand that sometime using Gevey SIM can be irritating that your iPhone can get signal but it will work as long as your current baseband is lower than 4.11.08.