Ringo is an international calling app (Low Cost International Calls) that converts your international calls to local calls and charges one of the cheapest call rates in the market. One of the best things about Ringo is that it works without the internet. So you don't have to worry about having a good internet connection, and can enjoy a good call quality with no lags at all. Ringo is available at http://www.ringo.co and on iOS, Android as well as Windows Store platforms.
