You can use Wi-Fi calling on your Sunbeam phone with T-Mobile service, it does not work with Verizon or AT&T.
To enable wi-fi calling you will first need to enable it on your T-Mobile account and provide them a 911 address. You may either contact T-Mobile or log in to your T-Mobile account to do so.
Next connect the phone to your Wi-Fi network and turn on Wi-Fi calling in the phone’s settings: System>Settings > Connectivity > WLAN > Wi-Fi Preferences > Advanced > Wi-Fi Calling > Enable Wi-Fi calling.
Done! You can now make calls over WiFi even if you do not have a cellular signal.