[G4 General] berkantkz:
* At the very beginning, I'd like to tell that I only have H815TR model. I don't know if there is any other variant(s) of G4 which supports VoLTE. If your device supports it, and VoLTE is missing for you too, after taking full backup, you may try as well but use the cust file from your backup you took before UsU'ing your device. I can say there is no risk(s) for like losing your imei, or hard brick etc.

This guide is only for Nougat stock/stock based(do not try on stock based roms until I update the thread. Someone reported something goes wrong w/ stock based roms) rom(s) and H815TR model. Why it is only for TR variant is that I do only have cust partition from TR model. Also, why this is for stock rom is that I've just found out a way to make them working and haven't tested with any other rom(s). As soon as I test, I'll add information about them and let you know.

Basically, here we do have 2 choices:

The first option

Use stock boot image with stock Nougat modem and the latest Lollipop baseband.

The second option (which I recommend)

Use stock Nougat modem and baseband with UsU kernel

The first way:

Download

Stock boot image

Stock modem image

Cust image

Latest UsU compatible baseband

Backup your boot image [optional but recommended]

Launch a command promt/powershell/terminal on your PC

Connect your phone to your PC and type following commands

adb reboot bootloader

fastboot erase boot

fastboot flash boot stock-nougat-boot-berkantkz.bin

fastboot erase modem

fastboot flash modem stock-nougat-modem-berkantkz.bin

fastboot erase cust

fastboot flash cust cust-berkantkz.bin

Disconnect your device, pull out the battery, and boot into TWRP

Flash "H815_UsU_baseband_flash-in-twrp.zip" and reboot

Skip to common steps

The second way:

Download

Stock modem image

Cust image

Latest UsU compatible boot image

Backup your boot image [optional but recommended]

Launch a command promt/powershell/terminal on your PC

Connect your phone to your PC and type following commands

adb reboot bootloader

fastboot erase boot

fastboot flash boot <downloaded-image-name>.img

fastboot erase modem

fastboot flash modem stock-nougat-modem-berkantkz.bin

fastboot erase cust

fastboot flash cust cust-berkantkz.bin

fastboot reboot

Skip to common steps

In common:

After your device boots up;

Go to mobile networks (hold down the mobile data icon in quick toggles)

Click on "Acces Point Names"

Open the menu and click on "Restore default settings"

Go back and enable VoLTE.

See the attachments for proof that proves it does work with UsU'd G4

Thanks:

@steadfasterX (for his suggestions, helps, and everything! You owe him for having an unlocked G4 w/ everything working!)

All should be fine now. Check both of them. Should you need any help, feel free to ask. I'll try to do my best. Please do not forget to leave me a thanks. That makes me happy :fingers-crossed:

Also, here I must inform you that if you had rooted your device with any root manager such as SuperSU, Magisk etc, you have to flash it again to have root access again. You have to do this since we erase and re-write boot images w/o changes those are required for root manager(s) to work.

Additional about VoWiFi (root required):

As @steadfasterX claimed and confirmed VoWiFi to work, use the commands below to enable it (I've personally tested but didn't work for me. It may depend on the operator and maybe the wifi you connected)

adb shell

su

setprop persist.dbg.wfc_avail_ovr 1