Sideline is designed to use the minutes from your carrier to let you place and receive calls. Included in the Sideline Subscription, you can use WiFi to connect calls over your internet connection as an alternative to using your cellular network.
When connected to WiFi, VoIP calling won't use up your minutes and will help you avoid any fees. You can find this in your Settings under "VoIP Calling".
Additionally, if at any time you are abroad, you can use WiFi to place calls to U.S numbers and not be charged for international calling fees or data.
Please note, turning this setting off will not cancel your subscription. It will only turn the setting off and use your carrier minutes.
To cancel this subscription, you will need to go to the App Store to avoid further charges.