True caller can install in very smartphones and true caller gives true details of callers of unknown calls with users name and location and also the sim operater user is using and how true caller get the details of every users I m telling you how they get the details if any smartphone installs the true caller app so all the contacts for smartphone goes to true callers server as it is name is saved in the mobile they show same name of the unknown calls as saved in the mobile in with app is installed so friend true caller gives true detail if any unknown call is comming to your mobile and data is on then true caller will tell name of the person calling to you from xyz state.best app for searching unknown calls.