Please see updated module in official Magisk Plugin Repo.
This module enables the VoLTE and VoWiFi options by editing build.prop.
Important: VoLTE/VoWiFi will not work if your carrier doesn't support it, even if you install this module.
XDA Thread: here
persist.dbg.ims_volte_enable=1
persist.dbg.volte_avail_ovr=1
persist.dbg.vt_avail_ovr=1
persist.dbg.wfc_avail_ovr=1
persist.radio.rat_on=combine
persist.radio.data_ltd_sys_ind=1
persist.radio.data_con_rprt=1
persist.radio.calls.on.ims=1
2017-08-02 (v1.1): Removed "persist.data.iwlan.enable=true" as this was reported to break WiFi calling on some carriers.
2017-08-01 (v1): Switched from using service.sh to system.prop
2017-07-31 (Beta): Initial commit.