You can send large amount of messages with no limits. It's available for all smartphone platforms including iPhone, Android, Windows Mobile, Nokia, Blackberry, Symbian. Everyone is using it because you don't have to go to a website to fill in details or confirm your identity to use it. It just needs your mobile number and you are done! WhatsApp supports many different message types, from simple text to pictures to audio files. Usually a MMS message would cost a fair bit of money to send, so the fact that these can be sent to as many customers and prospects as you like for free is great.