Seems like the smart thing to do. Update to 1.1.3 to unbrick iPhone then downgrade it to 1.1.2 and jailbreak it. Found at Crunchgear.

Lightbulb Unlock iPhone 1.1.3 bootloader 4.6 ok !
Hello all !

I can finally confirm about iPhone 1.1.3 unlocked ok at 8:30PM 15/01/2008 by our team and many help from GeoHot from US, Imth from VN, and some experts about iPhone from Hackint0sh forum ! Great thanks to those awesome guys.

This method is hardware method. So have to open phone.

Status now is:
- Unlock the iPhone with firmware 1.1.3 (baseband 4.03.13)
- Downgrade the phone to 1.1.2 then jailbreak it for normally using.
- Phone will work at: firmware 1.1.2 and baseband 4.03.13.

We are still researching on Unlock and keep the firmware 1.1.3 (mean jailbreak 1.1.3) …

Will upload here some proof clip.

Thanks.