What is Wi-Fi calling?
Wi-Fi calling is a technology that enables a smartphone user to make and receive calls over a wireless internet connection rather than over the typical cellular network connection.
Wi-Fi calling also enables sending and receiving text messages over a wireless connection (similar to iMessage on iPhone).
However, not all service providers allow Wi-Fi calling. Lots of prepaid carriers do not allow it. Ex: Straight Talk Wireless is one of the carriers that do not.
If you are unsure, please contact your cellular provider for details about your plan.