Do you get calls from unknown international or national landline numbers? Do you want to know their country, area or even their mobile carrier? Want a free of cost, ad-free, open source and easy to use app? Then this is the app for you! How to use 1. Just enter the phone number you want in the main screen with the appropriate prefix of the country! 2. The prefix is usually in the form of +xx or 00xx where the x is the digits of the country code. For example, Greece has the prefix +30 or 0030.