Q: Don't enable Wi-Fi calling on your Sprint iPhone or you won't be able to make calls as soon as you leave your Wi-Fi area.
I tried enabling Wi-Fi calling on my iPhone 6 on Sprint and as soon as I left my Wi-Fi area my phone wouldn't recive or make calls. I would just a error.
I called Sprint about this and informed them but, If this doesn't happen to you then just go to the Wi-Fi calling setting > Update Emergency Contact > Check Disable Wi-Fi calling. That should fix it!