Irate owners in Germany have started a petition requesting Voice over LTE and WiFi calling features to be enabled on their new OnePlus 6 devices. Both features have been available for German users ever since the OnePlus 2, but they are disabled on the OnePlus 6 German SKUs. This is made more strange by the fact that international OnePlus 6 SKUs are capable of both VoLTE and WiFi calling.
https://www.notebookcheck.net/OnePlus-6-now-available-in-white-WiFi-calling-mysteriously-absent-on-some-European-regions.307966.0.html