Updating jailbroken iphone 3g
Getting the device back into DFU mode would at least allow us to jailbreak the device, essentially bringing it back from its bricked state.
I've seen people getting stuck in recovery loops and be able to fix it just fine.
If you have older baseband, you can go straight to using ultrasn0w.
You can update to i OS 4.2.1 from i Tunes but this will update your baseband and require the use of the i Pad firmware.
Here are their comments on the matter: There’s an error in the bundle for the i Phone3GS 4.1 that prevents the new baseband from being used.