App that Allows for Free calls between 2 Callers Anywhere

We need an iphone app that allows users who have installed that app on the phone to call one another at no cost for incoming and outgoing calls between the callers. It shall be free totally for many hours as they talk non-stop, even if they are located from different countries. Also, we need to add a chat panel to allow users to turn on chat panel to type chat messages to one another via the phone. We can provide the graphics where you need.