The US embargo against Cuba.
Hey there! I think there is some confusion here. Stateside international calling is a feature you can ad to your account to get discounted rates when calling other countries from the US. The use of Wi-Fi calling to these other countries while in the US have no impact on the rates. If you are in Cuba, you can call the US at $0.00/min when using WiFi calling but calling Cuba from the US is going to have a per minute rate, Wi-Fi calling or not.