[Samsung Galaxy S7 Edge (Exynos) ROMs, Kernels, Rec] _alexndr:
Try to add more CSC features (e.g. marked in red in below example). Below is an example from CSC THL (VoLTE + WiFiCall support):

<?xml version="1.0" encoding="UTF-8" ?>
<SamsungMobileFeauture>
<Version>ED001</Version>
<Country>THAILAND</Country>
<CountryISO>TH</CountryISO>
<SalesCode>THL</SalesCode>
<FeatureSet>
<CscFeature_Common_DisablePhoneNumberFormatting>TRUE</CscFeature_Common_DisablePhoneNumberFormatting>
<CscFeature_Framework_EnableBidirection>TRUE</CscFeature_Framework_EnableBidirection>
<CscFeature_Framework_EnableThaiVietReshaping>TRUE</CscFeature_Framework_EnableThaiVietReshaping>
<CscFeature_SIP_EnablePreferredEnglishTypeAsUS>TRUE</CscFeature_SIP_EnablePreferredEnglishTypeAsUS>
<CscFeature_Sip_LangQwertyType4HwKey>HW_KEYBOARD_COUNTRY_TYPE_THAILAND</CscFeature_Sip_LangQwertyType4HwKey>
<CscFeature_FMRadio_FrequencySpaceAs>50</CscFeature_FMRadio_FrequencySpaceAs>
<CscFeature_FMRadio_DefaultChannelAs>87.5</CscFeature_FMRadio_DefaultChannelAs>
<CscFeature_Web_SetUAProfile>http://wap.samsungmobile.com/uaprof/uaprof.rdf</CscFeature_Web_SetUAProfile>
<CscFeature_Web_EnableAutoSimHomeUrlInProfile>TRUE</CscFeature_Web_EnableAutoSimHomeUrlInProfile>
<CscFeature_RIL_EnableRoamingIcon4NationalRoaming>TRUE</CscFeature_RIL_EnableRoamingIcon4NationalRoaming>
<CscFeature_RIL_ForceConnectMMS>TRUE</CscFeature_RIL_ForceConnectMMS>
<CscFeature_Web_EnableMenuConvertUnicodeToZawgyiFont>TRUE</CscFeature_Web_EnableMenuConvertUnicodeToZawgyiFont>
<CscFeature_Web_DisableMostVisitedHomepage>TRUE</CscFeature_Web_DisableMostVisitedHomepage>
<CscFeature_SNote_AddOnFontConfig>SEA</CscFeature_SNote_AddOnFontConfig>
<CscFeature_RIL_DisplayStkUssdDialog>TRUE</CscFeature_RIL_DisplayStkUssdDialog>
<CscFeature_Web_DisableMostVisitedHomepage>TRUE</CscFeature_Web_DisableMostVisitedHomepage>
<CscFeature_Wifi_CountryCodeDefaultFromCsc>TRUE</CscFeature_Wifi_CountryCodeDefaultFromCsc>
<CscFeature_Setting_IncludeApn4SwUpdate>TRUE</CscFeature_Setting_IncludeApn4SwUpdate>
<CscFeature_Contact_IgnoreSpaceDuringSearch>TRUE</CscFeature_Contact_IgnoreSpaceDuringSearch>
<CscFeature_Web_ConfigSyncSource>TRUE</CscFeature_Web_ConfigSyncSource>
<CscFeature_SmartManager_ConfigSubFeatures>roguepopup|autoclean|autorestart</CscFeature_SmartManager_ConfigSubFeatures>
[COLOR="Red"]	<CscFeature_IMS_EnableIMS>TRUE</CscFeature_IMS_EnableIMS>
<CscFeature_IMS_EnableVoLTE>true</CscFeature_IMS_EnableVoLTE>
<CscFeature_IMS_EnableLTEVideoCall>TRUE</CscFeature_IMS_EnableLTEVideoCall>
<CscFeature_IMS_FrameworkVersion>6.0</CscFeature_IMS_FrameworkVersion>
<CscFeature_RIL_SupportImsService>TRUE</CscFeature_RIL_SupportImsService>
<CscFeature_RIL_SupportVolte>TRUE</CscFeature_RIL_SupportVolte> [/COLOR]
<CscFeature_RIL_SupportSrvcc>TRUE</CscFeature_RIL_SupportSrvcc>
<CscFeature_RIL_SrvccRel>10</CscFeature_RIL_SrvccRel>
<CscFeature_RIL_BlockUssdDuringVolteCall>TRUE</CscFeature_RIL_BlockUssdDuringVolteCall>
<CscFeature_RIL_UseMpsForImsSetting>TRUE</CscFeature_RIL_UseMpsForImsSetting>
<CscFeature_RIL_E911RoutingPolicy>auto</CscFeature_RIL_E911RoutingPolicy>
<CscFeature_RIL_ConfigAlwaysOnApn>ims,xcap</CscFeature_RIL_ConfigAlwaysOnApn>
<CscFeature_RIL_ConfigSpecialPdpFlag>im_cn</CscFeature_RIL_ConfigSpecialPdpFlag>
[COLOR="red"]<CscFeature_SystemUI_ConfigDefQuickSettingItem>Wifi,SilentMode,Bluetooth,RotationLock,Flashlight,Location,MobileData,AirplaneMode,Performance,PowerSaving,Nfc,WifiHotspot,PersonalMode,UDS,BikeMode,BlueLightFilter,Aod,AllShareCast,SecureFolder,DeviceVisibility,Dnd,Sync,UltraPowerSaving,ScreenRecorder,VoLte</CscFeature_SystemUI_ConfigDefQuickSettingItem>[/COLOR]
<CscFeature_RIL_ConfigEpdgExtraFunction>ERIS,MobilePrefSim_52001_52003_52074_52054_52005_52000_52004;,ShowPrefModeMenuSim_52003_52001_52074_52054_52005_52000_52004;</CscFeature_RIL_ConfigEpdgExtraFunction>
<CscFeature_RIL_SupportEpdg>true</CscFeature_RIL_SupportEpdg>
<CscFeature_Common_ConfigEmergencyModePackages>com.ipsec.service,com.sec.android.providers.iwlansettings,com.sec.android.providers.mapcon</CscFeature_Common_ConfigEmergencyModePackages>
<CscFeature_RIL_SupportEpdgOnAirplaneMode>true</CscFeature_RIL_SupportEpdgOnAirplaneMode>
[COLOR="red"] <CscFeature_Setting_SupportWifiCall>true</CscFeature_Setting_SupportWifiCall>
<CscFeature_Setting_SupportWiFiCallingMenu>TRUE</CscFeature_Setting_SupportWiFiCallingMenu>[/COLOR]
<CscFeature_Common_SupportWcdmaInSlave>TRUE</CscFeature_Common_SupportWcdmaInSlave>
<CscFeature_VoiceCall_ConfigOpStyleForHdIcon>NOHD</CscFeature_VoiceCall_ConfigOpStyleForHdIcon>
[COLOR="red"]<CscFeature_VoiceCall_ConfigOpStyleForMobileNetSetting>voltesettingscommon,voltesettingEUR,voltesettingTHL</CscFeature_VoiceCall_ConfigOpStyleForMobileNetSetting> [/COLOR]
<CscFeature_NFC_ConfigDynamicFirmwareLoading>THL</CscFeature_NFC_ConfigDynamicFirmwareLoading>
<CscFeature_RIL_EnableCallBarringConnectToUssd>TRUE</CscFeature_RIL_EnableCallBarringConnectToUssd>
</FeatureSet>
</SamsungMobileFeauture>

IMO lines marked in red SHOULD be added to enable VoLTE/WiFiCall to /data/devbase/system/others.xml. Anyway - in my case only VoLTE button has been added (see attachment), I can't find WiFi calling... Probably it may depend on my operator which does not support WiFiCall, I'm not sure..