In the meantime, I have found out how to get VoLTE and VoWifi working, provided you have these functions from your mobile phone provider, otherwise these instructions may cause problems. The following commands can be executed via a terminal on a PC with ADB while the device is in recovery mode. This method works without root rights! While the device is switched on, you have to switch on the debugging mode via the developer options. And reboot the device in recovery mode: adb reboot recovery After that, you can enter the following commands once you are on the language selection screen: adb root adb shell setprop persist.dbg.ims_volte_enable 1 adb shell setprop persist.dbg.volte_avail_ovr 1 adb shell setprop persist.dbg.vt_avail_ovr 1 adb shell setprop persist.radio.VT_ENABLE 1 adb shell setprop persist.dbg.wfc_avail_ovr 1 adb reboot I take no responsibility for this workaround and only share it with people who know what they are doing and how to deal with ADB.