It has been 10 years since HTC already closed its business in Korea, so there is no Korean telecommunications company or supplier file, and it does not sell. It's sad. Anyway, let me explain. Originally, HTC products were not allowed to open Qualcomm ports, but only U12+ can open Qualcomm ports
(adb shell - su - setprop sys.usb.config rndis,diag,adb)
Volte in Korea is an independent tta-volte method, so I have the same Qualcomm Snapdragon 845 and I extracted efs files and mbn from Sony Xperia xz2 Korean version firmware, which was officially released in Korea, and pasted them using Qualcomm epsproler.
If the communication company you are using has its own standard like Korea, you can replace the efs file in the same way as I do, and if that doesn't matter, please read the following immediately.
Note the HTC system folder. There is a secret in the system custom folder. First, if you look at customize - MNS folder, it's a number.I see xml. There is a secret in that number. The number is the carrier code. It's very simple. I found this. It was such a pleasure. Please correct the xml title. For example, it is 45008 because it is KT(koreatelecom) mcc:450 mnc:08 You can check the carrier's mcc, mnc(apn) and modify it to 45008.xml and if you look in the custom folder, there is mns_map.xml. Edit the file as text If you enter the 45008th place you changed earlier and reboot, you will be able to create a volte active menu on the existing phone app setup screen.
This is all, simple. When you add an xml (app:mcc+mnc) title in the mns folder, write and save the number that was just added in the custom folder-mns_map_xml text editor, and reboot, the htc phone app settings show the volte activation menu, and there are no other changes to the build-prop In the case of Korea, it was necessary to modify the efs file because it is volte in a nonstandard way.
Modifying directly to root file editor without module It's very simple. My last hope is that volte is possible at gsi and that htc will continue to announce new flagships and that htc users are all healthy, thank you.
*To you in Seoul*