[OnePlus 5 Guides, News, & Discussion] dumdidum123:
After hours of trying to use several tutorials, guides, combining them etc. i finally managed to get Voice over LTE and Voice over Wifi working on my OP5 running LineageOS 20 for the first SIM Slot (not for the second one lol).

Root is available to me and required for my way i guess. I am using a german SIM from AldiTalk/MedionMobile (o2 network).

I just share what i did, maybe it helps someone.

First, backup of the EFS! (-> https://xdaforums.com/t/oneplus-5-u...ndroid-efs-backup-more.3624877/#post-72748932)

QPST PDC, EFS Explorer etc. have been installed for years on my computer from previous experiments, i think you might need it, to have the drivers installed.

In case you need to download it, check step 3 in this guide for the download links -> https://xdaforums.com/t/guide-activate-volte-vowifi-oos-11-ob1-ob2.4223967/

Also download EFS Modded 1.2 from there.

All the commands to enable the proper usb modes like

setprop sys.usb.config diag,serial_cdev,serial_tty,rmnet_ipa,mass_storage,adb

and other variants of that didn't work for me, so i looked around a little and found an app which does the job. Root required and it's made for ASUS devices, however it still works. Get AsusVoLTE-su_fixed.apk from ->

https://xdaforums.com/t/mod-ish-asusvolte-w-root-fix.4322877/

OxygenOS users can use their diagnostics app to enable these options i guess but i don't have that available on LineageOS.

Connect your device via USB, open the AsusVoLTE App and hit "Enable PDC".

You should now be able to run

EfsTools.exe efsInfo

and get some output like

Use serial port 'COM7'
Version: 1, MaxDirectories: 50, MapPathnameLength: 1024, MaxFileSize: 0, MaxFilenameLength: 768, MaxMounts: 36, MaxSymlinkDepth: 0

.

I now tried to stick to the guide from https://xdaforums.com/t/guide-activate-volte-vowifi-oos-11-ob1-ob2.4223967/ starting with step 7. It says "and make sure the mcfg_autoselect_by_uim file is there". I downloaded a pack of mcfgs/mbns from https://xdaforums.com/t/volte-vowifi-op5-5t-for-almost-all-carrier.3816516/page-12#post-82891677

There was no mcfg_autoselect_by_uim file inside that pack and since i didn't know where to get it, i just used the EFS Explorer to extract it from my device. Not really sure if that's the right way. Someone might want to verify that elsewhere before trying. It is however located under nv/item_files/mcfg.

Next step is to select a mbn you want to use. I cant really help others with this step. Years ago i used apac/vodafone/volte/india for my german o2/Alditalk SIM and it worked fine so i tried that again.

Running the first two commands from Step 7

EfsTools.exe writeFile -i mcfg_autoselect_by_uim -o /nv/item_files/mcfg/mcfg_autoselect_by_uim
EfsTools.exe writeFile -i mcfg_autoselect_by_uim -o /nv/item_files/mcfg/mcfg_autoselect_by_uim -s 1

works without any errors or output at all except from stating the used COM port.

EfsTools.exe uploadDirectory -i mcfg_sw.mbn -o / -v

runs without issues while

EfsTools.exe uploadDirectory -i mcfg_sw.mbn -o / -s 1

returns an error in between:

Processing 'C:\Users\x\AppData\Local\Temp\EfsTools\fwi3jlks.opr\ims' ...
Error on upload file '/ims/imshandoverconfig'. EFS error. Code = 26

I ignored that for the time and rebooted the device. I really don't remember if it was neccessary to hit "Enable Volte" in the Asus VoLTE App, however Voice over LTE and Voice over Wifi are now working for the left, the more inner SIM Slot. If i put the SIM in the right slot, VoLTE and VoWifi does not work. I guess that's because of the error. Not sure where that comes from. With OxygenOS there were no problems with VoLTE on the right SIM Slot.

How to check now? Use *#*#4636#*#*, select Phone information, select Phone 0 (or 1), hit the three dots and look for IMS service status. For me it says:

IMS registration: registered

Voice over LTE: Unavailable

Voice over Wi-Fi: Available

Video calling: Available

UT interface: Unavailable

When i switch off WiFi, Voice over LTE becomes Available and Voice over WiFi becomes Unavailable.

Unfortunately LineageOS does not show any indication (VoLTE or VoWIFI symbol) in the status bar but when you are calling "HD" will show up in the call app.

If anyone has input regarding the mcfg_autoselect_by_uim file and where that should come from, i am happy about every hint. Also i will be happy for all input regarding "EFS error. Code = 26". I could work around it by just using the other SIM Slot, but it still leaves me confused.