[OnePlus 8 Pro Questions & Answers] happiboi:
Here's the screenshot & writeup of what I did:

Here is some screenshots of 5G reception, VoLTE icon, VoWiFi icon & VoWiFi Calling while in aeroplane mode to confirm all these things are working!

https://imgur.com/a/tau5wyX

So what did I do? All credits go to this guy on XDA to get VoLTE & VoWiFi working: https://xdaforums.com/rog-phone-2/how-to/guide-enabling-volte-vowifi-v2-t4028073

For the TL;DR version, I did what I mentioned previously to get 5G going here:

https://forums.oneplus.com/threads/...pro-in-australia.1225092/page-2#post-21673760

https://forums.oneplus.com/threads/...pro-in-australia.1225092/page-3#post-21717398

Then to get VoLTE & VoWiFi working download these files:

EFS zip - https://drive.google.com/open?id=1PiVhB35MPx19sxqxQ4svgOvPXL1dxobt

MBNs zip - https://drive.google.com/open?id=1v8V281EkYGI_C1KeMqVni8L2qjQLdx5P

EfsTools 0.10 modded 1.2 - https://github.com/HomerSp/EfsTools...modded-1.2/EfsTools-0.10-modded-1.2-win32.zip

EfsTools 0.10 modded 1.1 - https://github.com/HomerSp/EfsTools...modded-1.1/EfsTools-0.10-modded-1.1-win32.zip

The reason I've linked both modded 1.1 & 1.2 is because 1.2 is the latest version and supports activation of 2nd SIM slot (but it errors for me so I used the modded 1.1 version but that only does SIM slot 1).

So steps:

- Enable the VoLTE/VoWiFi toggles first:

- Download the OnePlus Log Kit app’s APK from > https://downloadmirror.co/1MW9/com.oem.oemlogkit_1.0-1.apk

-Install the OnePlus Log Kit APK

- Open dialer, type in *#800# (If this doesn't do anything, just google search "Oneplus engineer mode apk", download and install it. Then retry)

- Click 'Enter' on the warning

- Select 'oneplus Logkit'

- Scroll down & select 'Function Switch'

- tick the VoLTE & VoWiFi switch options

- Then reboot.

- when your phone comes back after restart, in Settings > Wifi & network > SIM & network > SIM1 (and SIM2) > you should now see the 'Enhanced communications' area have the option to toggle on VoLTE/VoWiFi

Onto the actual making VoLTE/VoWiFi work:

- Unzip EfsTools into a directory

- Open command window on PC & navigate to the directory created in above step

- On your phone, go to dialer, type in *#801# - enter into it via 'engineer mode'

- Select "Rndis, diag switch" - ON (last time we selected "full port switch on")

- Then in the command window, you should be able to test connection to EFStools by typing "EfsTools.exe efsInfo"

- This should give some info & not any errors (mine was like 2 lines of information)

- Then the real fun begins.

- Extract the efs.zip from above download into the same directory as the EFStools (make sure the mcfg_autoselect_by_uim file is there - yes it's 0 bytes) and then run 2 commands:

- 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 (this one I couldn't get working - it's for SIM slot 2 & only works if usinf modded 1.2 version)

- should see 0 errors

- then open the MBNs zip & look for your carrier file. Ours are \aunz\<your carrier - e.g. mine is Telstra>\commerci\mcfg_sw.mbn

- copy this mbn file to the same dir as the EFStools, then run 2 commands:

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

- EfsTools.exe uploadDirectory -i mcfg_sw.mbn -o / -s 1 (again this one I couldn't get working - it's for SIM slot 2 & only works if usinf modded 1.2 version)

- If it worked your screen should spew out a load of output but no errors.

- Reboot your phone & if you already enabled the switches from my above mentioned post, you should see the VoLTE/VoWiFi icons like in the screenshots linked above.

Seems like a lot but that's literally step by step explanation & takes roughly 5-10 mins to do slowly.

Happy days - 5G, VoLTE & VoWiFi all working on our OnePlus 8 Pro =)