HTC 10 is one of the few devices that offer wi-fi calling on the unlocked variant. to turn off / disable Wi-Fi calling on HTC 10 with no carrier, do as follows:
1. Open the Dialer app on your HTC 10
2. Tap the 3-dot icon on the top right of the screen, and go the Settings.
3. Scroll down to the Enhanced Communications settings, and toggle off the Wi-Fi Calling option.
Note that, if you are using the carrier model of HTC 10, the settings for WiFi Calling feature may vary.