First announced in February, the deal set a stunning high-water mark for an acquisition of a venture-capital-backed technology start-up. Facebook paid about $13.7 billion in stock and $4.59 billion in cash. It's also awarding $3.5 billion in restricted stock to WhatsApp employees, including nearly $2 billion to Chief Executive Jan Koum and $1 billion to co-founder Brian Acton. WhatsApp is set to remain a separate unit from Facebook's core social network.
Koum, who is accepting the same $1 salary as Facebook Chief Executive
In April, WhatsApp said it had 500 million "regular, active" users with growing numbers from Brazil, Russia, India and Mexico.
WhatsApp charges users $1 a year to use the service after a 1-year trial and has pledged to avoid ads and gimmicks.
In February, Zuckerberg called WhatsApp the only popular app to have produced stronger engagement with users than Facebook itself. While future development plans haven't been announced, he recently said it would take years before WhatsApp became a "huge" business for Facebook.