TruPhone for iPhone

I read about an "app" for the iPhone called TruPhone. It allows you to make calls over the internet when you have a WiFi connection. We have a weak cell signal at our house. I downloaded TruPhone to my iPhone and tried it out using our home WiFi. The call was crystal-clear - far better than what I'm used to at home on the cell. Another plus is that we're going on a trip soon and may not be able