Wi-Fi calling is not set to On by default, so you need to do it yourself. Go to Settings, and tap on Phone, and set the Wi-Fi calling to On.
If you are having the issue with the Wi-Fi calling at your home network, restart your router. Once you do so, check if the Wi-Fi calling is working.
This can help as well: go to Settings, turn off Wi-Fi, and turn it on again. Sometimes, the simplest things solve the bug.
- Navigate to Settings
- Tap on general
- Choose Reset
- Reset Network Settings
Many times, when you have some kind of an issue with your iPhone 6, a restart will fix it, which is why you should try it. Press and hold the sleep/wake button, and drag the slider when appears. Your phone will be off. Do the same, to turn your iPhone 6 on.