THIS METHOD WON’T DOWNGRADE YOUR BASEBAND OR UNLOCK YOUR PHONE AGAIN
Preliminary reports say that the OS is downgrading but the modem firmware is not (aka, the modem firmware stays at 04.01.13_G instead of downgrading to 03.14.08_G). This allows use of Wi-Fi but not GSM functions (phone/edge/sms) unless you’re using AT&T. Note: this only applies to fresh out of the box 1.1.1 or phones upgraded from 1.0.2 that was never unlocked. 1.1.1 iPhones that were previously unlocked at 1.0.2 with methods that fake the bb firmware version will have their firmware version remaining at 03.14.08_G.
Read the full article by following the link below…
http://iphone.fiveforty.net/wiki/index.php/Downgrade_from_1.1.1_to_1.0.2