I have an iPhone 4 from Japan with the carrier SoftBank. I was using it with Gevey sim before, but due to my fault, I connected it to iTunes and updated both the firmware and software. Now, the phone is on the "factory screen", and I cannot even go to the home screen to see what software and firmware it has; but I believe it is upgraded to iOS 6.0.1 and firmware 4.12.02.
Is there any way I can "downgrade" the firmware, and use the Gevey sim as before, because the factory unlock for this carrier is way expensive. I would really appreciate comments and suggestions!