Hi guys, I messed up with my iPhone 4 after tweaking some of its components which needed a full restore in the end it to get it fixed. So I tried to restore my iPhone to iOS 4.3.5 but iTunes is preventing me to do it and it gives me error 20. I haven’t encountered this error before. Please help. Thanks.
Asked by: Dennis from Lincoln, Nebraska
Step 1: Download and install the latest version of iTunes from the link posted above.
Step 2: Reboot your Mac OS X or PC after the installation.
Step 3: Remove your SIM card (yes, your micro AT&T SIM card)
Step 4: Then connect your device to your computer, and iTunes will automatically launch.
Step 5: Now, allow iTunes to install the latest version of the firmware. After restoring it, your device will automatically restart since you don’t have SIM card on your device, iTunes will prompt you that your device is not activated.
Step 6: Just simply disconnect your phone, then insert the SIM card, and connect it back to your computer in order to activate it.
Step 7: iTunes would start again and it would guide you through the entire activation process.
That’s it. In this way you will be able to restore your iPhone without getting any error. If you are planning to jailbreak iPhone 4 on iOS 4.3.5, then you can use Redsn0w 0.9.8b4. Or, if you have saved SHSH blobs, then you can follow this tutorial on how to downgrade your iPhone using TinyUmbrella.