I have the ATT version, and no you cannot unlock bootloader, and they are sim free, at least mine is sim unlocked.
ATT XT1097, yes i did.
in case you want to try:
Itīs E460, am I able to root it even when the phone is dead?
could you flash the kdz with the LG Flash tool?
I had the same problem as yours, try getting download mode (remove battery press volume up and down buttons at same time and connect...