Facebook Inc. agreed to buy messaging company WhatsApp for $19 billion in cash and stock, a blockbuster transaction that dwarfs the already sky-high prices that other startups have been able to recently command. 
 
 The 55-employee company, which acts as a kind of replacement for text messaging, has seen its use more than double in the past nine months to 450 million monthly users. That makes its service more popular than Twitter Inc.,... ||||| SAN FRANCISCO (MarketWatch) -- Shares of Facebook Inc. FB, -2.65% fell in the extended session Wednesday after the social network disclosed it was buying messaging network WhatsApp Inc. for $16 billion in stock and cash. Facebook shares fell 5% to $64.57 after hours on very heavy volume. Facebook said it will pay $4 billion in cash and $12 billion in stock for the company, and agreed to an additional $3 billion in restricted stock units to WhatsApp's founders and employees to be vested over the next four years. The agreement also stipulates that Facebook would pay a break-up fee of $1 billion in cash and $1 billion in stock. 
 
 Read the full story: Facebook to buy WhatsApp for $16 billion-plus
– Facebook is apparently mighty impressed with WhatsApp, a messaging app for smartphones: Mark Zuckerberg's company announced today that it plans to buy WhatsApp for up to $19 billion in cash and stock. WhatsApp claims 450 million monthly users, and the deal is further proof that Facebook "is willing to pay huge sums to acquire rival apps that gain sway with consumers," says the Wall Street Journal. WhatsApp will continue to operate independently. Investors were apparently not so wowed—Facebook shares dropped about 5% in after-hours trading, notes MarketWatch.