Natetrue has posted on his blog that once you have updated your virgin iPhone to 1.1.3 a downgrade will brick your phone.
If your iPhone has never been unlocked, downgrading from 1.1.3 will leave you bricked until you upgrade back to 1.1.3, as far as I can tell. The phone (even with an authentic AT&T SIM) reports an Incorrect SIM while iTunes says there's no SIM at all, when you've downgraded back to 1.1.1 or 1.1.2 (1.0.x untested).
This does not apply to unlocked iPhones since the 1.1.3 baseband update fails when trying to update.
It is possible that this might change in the final firmware version; however, it seems more likely that this is yet another attempt by Apple to block unlocking procedures.
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If your iPhone has never been unlocked, downgrading from 1.1.3 will leave you bricked until you upgrade back to 1.1.3, as far as I can tell. The phone (even with an authentic AT&T SIM) reports an Incorrect SIM while iTunes says there's no SIM at all, when you've downgraded back to 1.1.1 or 1.1.2 (1.0.x untested).
This does not apply to unlocked iPhones since the 1.1.3 baseband update fails when trying to update.
It is possible that this might change in the final firmware version; however, it seems more likely that this is yet another attempt by Apple to block unlocking procedures.
Read More