Anyway, to start, a little disclaimer: I hold no responsibility if this method renders your phone completely useless, or burns and makes some nice fireworks. I'm simply writing this to document the process that worked for me. Use at your own discretion.
Dislcimaer 2: this method will wipe out your internal sdcard, apps data, everything! It'll restore the phone back to the way you got it from AT&T.
Note to linux users like myself: get your a** on windows or run it from a VM. VirtualBox with Win7 works fine.
1. LGFlashTools v1.5. Anything less won't work. Mirror: HERE
2. DLL file for LGE980
4. The stock image file
Thanks to IOMonster for hosting these biga** files.
1. Install the LG drivers downloaded above.
2. Install LGFlashTools v1.5 (but don't run it)
3. Extract the DLL and the TOT files from above and put them in a nice tidy directory
1. Put the phone into download mode. (Turn off device, keep pressing volume down while plugging in the micro usb cable. If this doesn't work, try holding both volume keys instead)
2. Let the phone initialize and install the drivers. Once done, in Device manager, you should see the LG phone listed under COM ports (something along these lines).
3. Find that LG entry in Device Manager, click on Properties, Advanced and then change the COM port to COM41 and close/save.
4. Unplug your phone! Important step.
To get this tool to work, you'll need to do a few tricks.
1. Set the computer's date to some time in July 2012 or before.
2. Disconnect the internet
3. Find a serial number or register key from somewhere on the web (a google search for lgflashtools serial will yield some results). Can't help you here and please don't share any keys in this thread or get us in trouble.
4. Execute the LGFlashTools. It should ask you for a key, put it in. Now you should see a dialog where you can load the DLL file and the TOT files that you extracted earlier. Put them both in here. Click ok
5. There is a yellow arrow on the top left. Click on it to initialize the process. Once done, it should say "ready/finished" or whatever.
6. Put the phone in download mode again, and plug it into the USB port. LG FLash Tools should start flashing it automatically. When it's done, it'll automatically reboot into your stock AT&T rom and all of your data and internal sdcard files are gone.