[T-Mobile LG G4] objecttothis:
There are other threads about this but rather than pollute them with my post I figured I'd create a new thread to share my experience.

READ THE WHOLE THREAD BEFORE ATTEMPTING THIS. I AM NOT RESPONSIBLE IF YOU SCREW UP YOUR PHONE.

Feel free to comment and I will make adjustments to the op.

Pre-requisites

- LG G4 T-Mobile Variant (H811).

- The Phone must be paid in full.

- The account the phone is/was attached to needs to be in good standing.

- Proof of your purchase of the phone (eBay or paypal receipt)

- The phone must not be reported lost, or stolen.

- Try the T-Mobile Device Unlock and select permanent unlock (if it works skip to the section on retaining SIM Unlock)

- Persistence, patience and politeness.

History

I purchased a used LG G4 (H811) on eBay, then called T-Mobile to request the device unlock. I was told by two Customer Service representatives and two supervisors the same thing:

- I either had to get a T-Mobile account and register the device on their network for 40 days and request the device unlock.

- Or the original owner had to request the unlock.

T-Mobile would not budge, but you can make them give it to you. The CTIA Consumer Code for Wireless Service (http://www.ctia.org/policy-initiatives/voluntary-guidelines/consumer-code-for-wireless-service) is a Voluntary document drafted by the FCC and administered by CTIA that T-Mobile is a signer on. In section 12 it states that wireless providers will unlock eligible phones for customers, former customers and individual owners. That third category is the one that most of us fall into. Principle 2 of that section says that for post paid phones the provider will unlock them upon request for phones from accounts in good standing that have been paid off again for customers, former customers and individual owners. CAVEAT: The Code does allow them to charge you a "reasonable fee", but I was never asked to pay a fee.

Penalty for T-Mobile not complying is revocation of their status of meeting this code and they cannot display the seal which means other providers will harp on that and T-Mobile doesn't want that. After sharing this information with the supervisor they told me that I could write a letter to their legal department which I did not want to do.

Getting the SIM unlock code

1- Contact T-Mobile to request the device be unlocked. Unless they change their policy they will likely tell you the same thing they told me.

2- Go to FCC.gov and filed a complaint online stating that you are an individual owner of an eligible phone (T-Mobile never disputed that) and that T-Mobile was refusing to unlock it and therefore in violation of the CTIA code.

3- Go to CTIA.org and use the contact us link to send them a very similar email.

4- Finally go to bbb.org and filed a complaint online against T-Mobile USA (Make sure that you select the head office in Washington State).

In all three I provided my IMEI number for reference (#*06#) and THE SAME DAY I got an email from the Office of the President of T-Mobile requesting contact information to verify eligibility of the phone. I responded back and answered their questions. They needed the IMEI, make, model and receipt showing purchase. She then sent me an email telling me that she removed the block on their server from the app working and allowing a permanent unlock.

SIM Unlock procedure

1- If you are already running any flavor of the stock firmware that still has the T-Mobile unlock app then skip to step 6. If you are on a custom ROM reboot into TWRP and do a complete backup of everything EXCEPT your efs partition. If you later restore your efs partition after unlocking the phone it becomes locked again.

2- In TWRP wipe the device with the default settings.

3- Install a stock flavor ROM that still has the T-Mobile Unlock App.

4- (Optional) Install SuperSU to keep root.

5- (Optional) For good measure flash TWRP recovery in case the ROM you installed replaced the recovery.

6- Boot the T-Mobile Stock ROM and run the T-Mobile Unlock App. Request a permanent unlock and it should successfully unlock the phone.

7- Reboot and test with a non-T-mobile sim.

If you are satisfied with running the stock T-Mobile firmware then you're done. If you, like me want to run a custom ROM, then follow below.

The steps below assume you have a custom recovery and unlocked bootloader already

, but if not you can look at the threads on this forum on how to unlock your bootloader permanently, root, install custom recovery and install a custom ROM.

1- Turn off the phone.

2- Hold the volume down + power button.

3- When you see the LG logo release the power button for 1 second and then hold it again.

4- You will get a white screen asking if you want to factory reset the device. Select Yes, then Yes again and it will boot you into TWRP.

5- Back up your device (especially the EFS partition), but you need all of it. Use the file manager to move that backup to your external SD card.

6- Perform a standard wipe in TWRP.

7- Restore your backup of your custom firmware but DO NOT restore the efs partition or your device will again be SIM locked.

8- Restart.