How can I downgrade my iPhone's carrier version from AT&T 8.0 to AT&T 4.0?
My iPhone 3G is on 4.1, jailbroken, and it has the 06.15.00 iPad baseband. I need to downgrade its carrier version from AT&T 8.0 to AT&T 4.0, which is shown when I go into Settings>General>About and look in the Carrier field. I tried downloading an .ipcc file for AT&T 4.0 and I used iTunes to install it on my iPhone but the carrier version didn't change. How can I change my phone's carrier version?
I need to downgrade because my SIM card won't work without AT&T 4.0 settings.
If I unlock with ultrasn0w, then instead of "AT&T 8.0" I have "Carrier 8.0" and it still doesn't work.