Downgrade from 1.1.1. back to 1.0.2. with IPSF Unlock
I'm back from the dead!
I have just downgraded my 1.1.1 iPhone to 1.0.2. Without even attempting to downgrade the BB (not required for IPSF), I reinstalled all my apps and re-ran the IPSF application with the AT&T SIM card in the phone. The app reported that it was already unlocked.
Quickly replacing my AT&T Sim with my MNO's SIM card, the phone immediately re-activated.
Thus, the moral of the story is that for IPSF unlocked phones, no BB flash is required!