Activating the Android 5 native SIP client

Android brought a native SIP client with version 2.3, which some carriers/phone manufacturers disabled. You can re-enable it in Android 4 by setting some values in /system/build.prop. I do have a Android 5 phone (Wiko Rainbow UP), and there are no SIP settings in sight. build.prop does not contain the ro.config.hw_support_ipcall=true ro.config.hide_sipcall=false settings. How can I enable the native VoIP client on Android 5?