WhatsApp is a cross-platform instant messaging service for smartphones that relies on the internet for the transmission of messages. As of April 2014, the mobile messenger has more than 500 million monthly active users worldwide and ranks as one of the most popular mobile social apps globally.
Based on a low-cost subscription model, WhatsApp is a cheap alternative to carrier-billed text messaging via SMS, especially for international or group messaging. The mobile messaging app enables users to share text, image and video messages – the service handles more than 600 million photo and 64 billion overall messages every day. In the United States, the daily engagement rate among Android WhatsApp users was 36 percent.
Recent market data indicates that the majority of WhatsApp users in the United States are aged between 25 and 34 years and that the app enjoys a strong U.S. Hispanic user base.
Source : Statistics and facts about WhatsApp