Long story short, I bricked my lg g2 d801 after flashing twrp recovery and trying to flash custom rom. The phone would restart randomly. I had no connection and the signal bars crosses out in red. In settings most of my info like baseband, imei etc were missing. I was looking up and many people bricked their phones with no EFS backup to restore the IMEI. This is how I fixed my phone. This should also help people who have zeroed out IMEI after bad flash or whatever reason. But you should at least have IMEI number ready (from your box/ receipt or call t-mobile)
1. Flashed the phone to factory firmware using LG support tool. I used the following guide:
used the firmware: T-Mobile KitKat D80120A_00.kdz
there's also similar guides in xda, follow whichever you prefer. Goal is to revert the phone back to stock.
After flashing the phone, the phone was woking; however imei was null. In phone settings my IMEI was 0. To fix the null/bad imei follow this guide (Not all the steps are my work; this guide helped me http://forum.xda-developers.com/show....php?t=1942417
, also watched some you tube videos):
2. You need the following drivers and software:
imei converter: http://www.sendspace.com/file/a3spfh
3. After installing the driver; turn on USB debugging and connect the phone to computer
4. Install QPST, run QPST configuration from from start menu
5. Click on Ports tab. Click Add new port. Your phone should be COM4/5. It will say USB after the port. Select the port and click OK.
6. The port should come up on active phones. Select the phone and and click on "Software Download" from start clients menu
7. Click on Backup tab. Your port should appear. Backup by clicking on start
8. Now go to Program Files/qualcomm/qpst/bin folder
9. Run RF_NV_Manager program
10. Click File read from phone. Your IMEI should appear on number 550; NV_UE_IMEI_I
11. In my case; there was no item 550 as my IMEI was missing. Don't worry.
12. Click on file> Read supported RF NV items
13. Now click on item 550. It should show 9 blank fields.
14. Start IMEI converter. Type in your IMEI in enter IMEI click on convert IMEI
15. There will be 18 digits in groups of 9
18. In RF_NV_Manager program; click on Hex by Write NV button
19. IN the 9 boxes; type in the numbers from IMEI converter starting from left. Type in first group of two numbers in the first field, then go to the next field and type in second 2 digits
20. After you fill in; click on write NV
21. Now click on File> Read from phone. NV item number 550 should appear now.
22. Unplug, Restart your phone and your IMEI number should be there and phone should connect to network.
Above process fixed my phone with full 4G LTE data. Now depending on the how bad your EFS was damaged; you might not get 4G lte data. But at least now; you will be able to send the phone back to LG for repair or return to t-mobile as IMEI number will be in your phone.