When it comes to the name facebook, I think everyone know it, as the facebook added its app messenger so that facebook can be used on phone easily . facebook messenger is one of the most downloaded app, and its really worth it, its very simple to use, also easy to download and install, and can use the same id as we use on facebook . this is the best way to stay online all time, also can get instant messages, and other updates, . it can be used for voice or video calling over facebook from mobile phone . and this app is totally free . it is supported by all android, ios and other systems .