Voice or video calls through Tango work over the Internet, so your international call rates will not apply, but you may be charged for the Internet data by your operator.
Using a free Wi-Fi hotspot to place voice or video calls is absolutely free. When you place voice or video calls over the 3G or 4G network, your charges will be based on the data plan you have set up with your mobile provider. Be sure to check with your mobile provider regarding any fees for using your data allowance.
Tango does not use your mobile provider monthly minutes so there are no extra fees or international charges when calling a friend down the street or a family member in another country.