Free is Good
Not only is WhatsApp free to download and use now, it also has its own built-in feature to allow for free phone calls to other fellow WhatsAppers with data usage. This is a great way to get around horrible long distance or international fees. Nothing special is required to access data-to-data calling, just that both callers are using their data line and that they know their data plan to avoid any expensive mistakes. You may not, however, use this method to use emergency services, though.