WhatsApp Messenger is the world's most popular instant messaging app for smartphones.
You can use it to send and receive text and voice messages, photos, videos, even call your friends in other countries, and because it uses your phone's internet connection it might not cost you anything at all (depending on whether you'll pay data charges).
It's easy to set up and use. There's no need to create and remember new account names or pins because it works with your phone number, and uses your regular address book to find and connect you with friends who use WhatsApp already.
You can talk one-to-one or in group chats, and because you're always logged in there's no way to miss messages. Even if your phone is turned off, WhatsApp will save your messages and display them as soon as you're back online.
There's plenty more (location sharing, contact exchange, message broadcasting) and the app is free for a year, currently $0.99/ year afterwards.
What's New in Version 2.17.41
• Pin chats to the top of your chat list, so you can quickly find them. Just swipe right on a chat and tap the pin icon.
• You can now send documents of any type. To send a document, open a chat, tap attach — document.
• When you receive multiple photos, you can now tap and hold on the group of photos to quickly forward or delete all of them.