When you make or receive calls on your cellular network, you will be using minutes from your cellular phone plan.
When you make or receive calls on your home wireless network, you will be using your home internet data.
If you are on public WiFi, you will be using data associated with their connection.
You can change which connection the Cloud Phone app uses under Settings>Account in the app. Next to “Make calls using” you can choose between Wave Phone, Cell Phone, or Always Ask.
This setting will also be listed in small print at the top of the dialer before you make a call.