Wikipedia
Voxofon
Founded in 2008, Voxofon provides mobile apps and communication services utilizing over-the-top (OTT) voice and messaging technologies for smartphones, tablets, and web applications. Voxofon is used to make free app-to-app domestic and international calls and texts as well as make cheap international calls and texts to friends and family that use feature phones or landlines. The Voxofon app is a cross-platform application that is supported on iPhone, iPod Touch, iPad, Android, Blackberry, Windows Phone, and through any web browser.
The Voxofon app can connect calls and send texts through the voice network, 3G/4G, or WiFi depending on the user settings and preferences.