Whatsapp-      In June 2009, Apple launched push notifications, letting developers ping users when they were not using an app. Koum updated WhatsApp so that each time you changed your status it would ping everyone in the user's network. WhatsApp 2.0 was released with a messaging component and the active users suddenly swelled to 250,000. Koum visited Brian Acton, who was still unemployed while managing the unsuccessful start up, and decided to join the company. In October Acton persuaded five ex-Yahoo friends to invest $250,000 in seed funding, and as a result was granted co-founder status and a stake. He officially joined on November 1.^[7] After months at beta stage, the application eventually launched in November 2009 exclusively on the App Store for the iPhone. Koum then hired an old friend who lived in Los Angeles, Chris Peiffer, to make the BlackBerry version, which arrived two months later.^[7]
WhatsApp was switched from a free to paid service to avoid growing too fast, mainly because the primary cost was sending verification texts to users. In December 2009 WhatsApp for the iPhone was updated to send photos. By early 2011, WhatsApp was in the top 20 of all apps in the U.S. App Store.^[7]
The founders agreed to take $7 million from Sequoia Capital on top of their $250,000 seed funding, after months of negotiation with Sequoia partner Jim Goetz.^[7]
By February 2013, WhatsApp's user base had swelled to about 200 million active users and its staff to 50. Sequoia invested another $50 million, valuing WhatsApp at $1.5 billion.^[7]

hi friends
WhatsApp Messenger is a proprietary, cross-platform instant messaging subscription service for smartphones and selected feature phones that uses the internet for communication. In addition to text messaging, users can send each other images, video, and audio media messages as well as their location using integrated mapping features.
WhatsApp Inc. was founded in 2009 by US citizens Brian Acton and Jan Koum (also the CEO), both former employees of Yahoo!, and is based in Mountain View, California.^[1][2] The company employs 55 people.^[3] The company is currently in the process of takeover after Facebook Inc. announced its acquisition of WhatsApp Inc. on February 19, 2014, for US$19 billion.^[3][4]
In a December 2013 blog post, WhatsApp claimed that 400 million active users use the service each month.^[5] As of 22 April 2014, WhatsApp had over 500 million monthly active users, 700 million photos and 100 million videos are shared each day, and the messaging system handles more than 10 billion messages each day.