Googal duo is a HD vedio calling app which is lounched by googal.i m using this app its usefull it is based on signal strenth if u want to vedio call on duo than u have to have a 3G or 4G net. U cant make vedio call on 2g signals. If u r using 4g net and u makes the call it will feel look like a live u talking. pretty gud app for 3g or 4g users