WhatsApp uses your phone's Internet connection (4G/3G/2G/EDGE or Wi-Fi, as available) to send and receive messages to your friends and family. You do not have to pay for every message. As long as you have not exceeded your data limit or you are connected to a free Wi-Fi network, your carrier should not charge you extra for messaging over WhatsApp.
WhatsApp Calling works in the same way. Learn more about WhatsApp Calling on: Android | iPhone | Windows Phone
Please be aware that:
- If your phone is roaming, additional mobile data charges may apply. Learn how to configure roaming settings for WhatsApp on: Android | iPhone | Windows Phone | Nokia S40
- If you send SMS messages to your friends inviting them to use WhatsApp, service charges from your mobile provider may also apply.