[OnePlus 8T Guides, News, & Discussion] 21prods:
Enable VoLTE and VoWiFi on OnePlus 8T on a Custom ROM (LOS 20 / Android 13 - OOS13)

This guide is made for those people who, like me, find themselves not being able to make use of VoLTE or VoWiFi, even though these options are enabled in LOS 20.

This guide will help you unlock VoLTE and VoWifi and doesn't require root access (well, not exactly, you'll see).

I'm NOT responsible to any damage you make to your phone. I would say there's barely any chance to damage anything, but I don't know, I'm not an expert, you've been warned.

All Qualcomm necessary files can be downloaded from here: https://www.mediafire.com/file/c59zj43e7d3x1pl/Necessary+Files.zip/file

Once downloaded, open the ZIP file and install QPST_2.7.4.96. Now, within the same ZIP you downloaded, head to Qualcomm Drivers, copy the "Mi5_Qualcomm_Drivers" to your desktop.

Once on your desktop, plug in your phone to your PC, make sure USB debugging and Rooted debugging are enabled (this option is available in LOS, I guess other Custom ROMs will offer it, as well, I don't know).

Download the file EfsTools-0.14.zip from here: https://github.com/JohnBel/EfsTools/archive/0.14.zip

Download and install .NET 5.0 Desktop Runtime (v5.0.5) - Windows x64 , required for the EfsTools.exe program to work from previous point.

Now we are ready to go:

1. Open a Terminal window and type the following code one line at a time:

2. Go to Control Panel – Device Manager .. you will see two unknown device.

Right click on the first one – Update Driver – browse my computer drivers

Let me pick form a list of available drivers- click on Have Disk ..- show all devices

When the locate file window appears, navigate to the "Mi5_Qualcomm_Drivers" folder you extracted to your desktop earlier.

Open the "qcmdm.inf" file.

When you return to the previous "Install from disk" window press Ok.

Once that window closes, you should be at the previous "Select the device driver you want to install for this hardware" window

On the left side, make sure to select "Qualcomm Incorporated", on the right, scroll down until you find "Qualcomm HS-USB Android DIAG 9018" click it, and press next.

Then do the same to the other unknown Driver.

3. Once you have done the steps above, open QPST config.

4. Note down COM# of SDX55M device.

5. Connect the phone to the computer. Go to the EfsTools-0.14 folder, open a command window.

6. Check if EfsTools.exe sees your device by entering EfsTools.exe targetInfo or EfsTools.exe efsInfo. Everything goes ok if the output is something like this:

If an error occurs:

then you need to change <efstool port = "auto" in file EfsTools.dll.config to the number that the QPST showed for SDX55M device. For example: <efstool port = "COM7"

7. Put the correct mcfg_sw.mbn in the EfsTools folder. In my case (Spain-Movistar), I had to extract the file from the OOS13 for the Oneplus 10Pro, or I would not get VoWiFi (modem.img /image/modem_pr/mcfg/configs/mcfg_sw/generic/EU/Telefonica/Commercial/Spain/).

8. Type the following code one line at a time:

It will take a minute or so, but you shouldn't see any error message.

9. Type:

That's it.

I've been able to write this guide thanks to a lot of work of other users who posted other guides, but which helped me a lot to find a solution for my device.

In particular, I want to thank @jimmy123322 @yegg55 and @rmendez011