It's possible to make phone calls to any phone number (not just 911) underground today over the wifi with the Big 3 today via Wifi Calling if you have a VPN (BAI might be blocking it if you don't use one, idk).
Wi-Fi Calling from Bell Mobility allows you, when your phone is connected to a Wi-Fi network, to make and receive calls, as well as send and receive messages.
www.bell.ca
Stay connected wherever you are with WiFi Calling. Make or receive phone calls and send text messages wherever there’s a WiFi connection. Learn more about WiFi calling.
www.rogers.com
If you don't have Wi-Fi, then there's less of a backstop for people with other carriers (if those other carriers don't participate).