Facebook has just announced that they're buying the popular instant messaging (IM) app WhatsApp for an incredibly cool 19 billion-with-a-b dollars. That's $4 billion in cash, $12 billion in shares, and $3 billion in restricted stock for the founders and employees that'll divest over the next 4 years. So why is Facebook spending all this money on WhatsApp and what are they getting for it?

Facebook, of course, has their own popular IM app, Facebook Messenger, just like they had their own photos platform before they bought Instagram. Like Instagram, WhatsApp will remain its own app, and be run independently from Facebook. That will either maintain options or fragment resources, depending on how you look at it.

There's also a huge overlap between social networks and instant messenger apps in general. Arguably, social networks rose from older instant messenger apps, then went full circle and became them, at least in part. IM is huge business, hot business, and growing business. Many companies never see their replacement — or obsolesce — coming. Facebook seems intent on not making that mistake and clearly have the bank account to back it up.

The problem with trying to buy your potential replacements in the market is that it's infinitely expensive. There's always the next maybe-big-thing coming. Will WhatsApp end up really being worth $16 billion to Facebook, especially in a volatile market that includes other major players like Line, WeChat, BBM, and many more?

Time will tell, but read the full press release below and tell me what you think...

Update 1: WhatsApp blog post is now live.

Update 2: Mark Zuckerberg has posted about the deal now as well.

Facebook to Acquire WhatsApp

Acquisition accelerates Facebook’s ability to bring connectivity and utility to the world Leading mobile messaging company will continue to operate independently and retain its brand WhatsApp co-founder and CEO Jan Koum to join Facebook Board of Directors

MENLO PARK, CALIF. – February 19, 2014 – Facebook today announced that it has reached a definitive agreement to acquire WhatsApp, a rapidly growing cross-platform mobile messaging company, for a total of approximately $16 billion, including $4 billion in cash and approximately $12 billion worth of Facebook shares. The agreement also provides for an additional $3 billion in restricted stock units to be granted to WhatsApp’s founders and employees that will vest over four years subsequent to closing.

WhatsApp has built a leading and rapidly growing real-time mobile messaging service, with: Over 450 million people using the service each month; 70% of those people active on a given day; Messaging volume approaching the entire global telecom SMS volume; and Continued strong growth, currently adding more than 1 million new registered users per day.

The acquisition supports Facebook and WhatsApp's shared mission to bring more connectivity and utility to the world by delivering core internet services efficiently and affordably. The combination will help accelerate growth and user engagement across both companies.

"WhatsApp is on a path to connect 1 billion people. The services that reach that milestone are all incredibly valuable," said Mark Zuckerberg, Facebook founder and CEO. "I've known Jan for a long time and I'm excited to partner with him and his team to make the world more open and connected."

Jan Koum, WhatsApp co-founder and CEO, said, “WhatsApp's extremely high user engagement and rapid growth are driven by the simple, powerful and instantaneous messaging capabilities we provide. We're excited and honored to partner with Mark and Facebook as we continue to bring our product to more people around the world.”

Facebook fosters an environment where independent-minded entrepreneurs can build companies, set their own direction and focus on growth while also benefiting from Facebook’s expertise, resources and scale. This approach is working well with Instagram, and WhatsApp will operate in this manner. WhatsApp’s brand will be maintained; its headquarters will remain in Mountain View, CA; Jan Koum will join Facebook’s Board of Directors; and WhatsApp’s core messaging product and Facebook’s existing Messenger app will continue to operate as standalone applications.

Upon closing of the deal, all outstanding shares of WhatsApp capital stock and options to purchase WhatsApp capital stock will be cancelled in exchange for $4 billion in cash and 183,865,778 shares of Facebook Class A common stock (worth $12 billion based on the average closing price of the six trading days preceding February 18, 2014 of $65.2650 per share). In addition, upon closing, Facebook will grant 45,966,444 restricted stock units to WhatsApp employees (worth $3 billion based on the average closing price of the six trading days preceding February 18, 2014 of $65.2650 per share). As of February 17, 2014, Facebook had 2,551,654,996 Class A and B shares outstanding plus approximately 139 million dilutive securities primarily consisting of unvested RSUs. The Class A common stock and RSUs issued to WhatsApp shareholders and employees upon closing will represent 7.9% of Facebook shares based on current shares and RSUs outstanding.

In the event of termination of the Merger Agreement under certain circumstances principally related to a failure to obtain required regulatory approvals, the Merger Agreement provides for Facebook to pay WhatsApp a fee of $1 billion in cash and to issue to WhatsApp a number of shares of Facebook’s Class A common stock equal to $1 billion based on the average closing price of the ten trading days preceding such termination date.

Facebook was advised by Allen & Company LLC and Weil, Gotshal & Manges LLP; and WhatsApp was advised by Morgan Stanley and Fenwick & West, LLP.

Webcast and Conference Call Information

Facebook will host a 30-minute conference call to discuss the acquisition at 3:00 pm PT / 6:00pm ET today. The dial-in number for the call is (866) 751-3284 (toll free) and (973) 935-8772 (international), conference ID: 2907041. The live webcast of the call can be accessed at the Facebook Investor Relations website at investor.fb.com. Facebook uses the website http://investor.fb.com as a means of disclosing material non-public information and for complying with its disclosure obligations under Regulation FD.

Following the call, a replay will be available at the same website. A telephonic replay will be available for one week following the conference call at (855) 859-2056 or (404) 537-3406, conference ID 2907041.