How To Downgrade Baseband 4.12.02 to 01.59.00 on iPhone 4:
People who updated their iPhone 4 to iOS 6.0 unintentionally lost their unlock
(GEVEY SIM). There’s still no unlock available for Baseband 4.12.02 but
there’s a solution for that. As Apple is still signing their previous version
of iOS, iOS 5.1.1 you can still downgrade your iPhone 4 to baseband 04.12.01
which is unlockable with Gevey.
Things you will be needing during this process:
- A restore copy of iOS 5.1.1
Before you downgrade, please remember you can only downgrade your iDevice firmware if, and only if, you have saved your SHSH blobs somewhere safely, hopefully with Saurik’s Cydia server, or locally on your machine.
From now on, I will assume you have saved your blobs on Saurik’s Cydia server.
STEP 1: To start with, you need to make sure you have a copy of iOS 5.1.1 or whatever firmware you need to downgrade for your device which you can find and download from here.
STEP 2: Next, you need to make sure your hosts file is pointing to Saurik’s server, and not Apple’s. If you haven’t done this then please check this guide.
Alternatively, use TinyUmbrella to make iTunes look at Cydia’s Server in the Advanced options.
STEP 3: Now plug in your iOS device, and switch it off, but leave it plugged in.
STEP 4: Put your device into DFU mode, our guide here.
STEP 5: Select your firmware manually to restore to. (Shift on Windows, and option on a Mac)
But, should your phone should now have an error, such as error 1015, DO NOT PANIC! This is normal and has a quick fix. Just download anduse Recboot to kick it out of recovery mode – check guide