You will need:
LG United Drivers: Download the latest from LG homepage and install it.
The EXACT IMEI numbers from your phone, located at tag under battery space (don't try to 'clone' or use another: don't work and it's illigal).
Rooted phone (not sure about this, mine already rooted)
Preparing the arena. Let's go:
A1. Plug the phone and let windows recognize it.
A2. Make sure two devices are present: 'LGE AndroidNet USB Modem' under "Modems" section, and LGE 'Androidnet USB Serial Port' under "Ports" section.
A4. Activate USB Debbugin in Settins
A5. Plug again
A6. PC will recognize another device, make sure: 'AndroidNET Sooner Single ADB Interface' under "ADB Interface"
Now, the fun begins: lets write the IMEIs!
B1. Plug your phone to PC and select LG Software
B2. Go to Device Manager and get the COM number from 'LGE AndroidNET USB Serial Port'
B3. Dial 3845#*455# (the last 3 numbers depends on your model)
B4. Select Settings
B5. Seletc Diag Settings
B6. Seletc UART Set for Diag
B7. Go Back
B8. Select Data Settings
B9. Select UART Set for Data
B10. Go back
B11. Open Putty and select "Serial"
B12. Write the COM port you get on step B2 (ex.: COM6) in the proper field. Click OPEN
B13. Type AT and hit ENTER. You should get an 'OK'. If not, check the COM port number (If you don't get any letter while typing, type ATE1, hit ENTER. You should see 'OK')
B14. Type at%imei=x,x,x,x,x,x,x,x,x,x,x,x,x,x,x (with the commas), where x,x,x... is your orginal IMEI number. It should response IMEI WRITE OK
B15. Type at%imei2=x,x,x,x,x,x,x,x,x,x,x,x,x,x,x (with the commas), where x,x,x... is your orginal IMEI number. It should response IMEI WRITE OK
B16. Close PuTTy terminal
B17. Reboot phone
I still don't have the "efs" folder, so maybe this is only a workaround. Also, I don't know if I flash a firmware I will lost IMEIs again.
But phone is working now. Calls, SMS, 3G... everything!