There is a cross platform application available that allows you to send messages for free from any phone to any phone, just using the Internet data connection of your phone. It very convenient and practical, in their words, “Awesome. Cross-platform. Now with group chat”.
Basically it works like a chat room, such as Messenger or Skype, but you will found it more convenient and practical in its use. The application is called WhatsApp and one of its most interesting features is that it is necessary to open the application to receive messages through this channel: When your contact sends you a message through WhatsApp, you will receive a notification the same as you get when you have sent a text message, with the difference that displays the application icon in the notification WhatsApp.