At one point or another, it's been the number one paid app in 131 markets globally. Depending on who's estimating, it has anywhere between 200 and 350 million users around the world. Barcelona's coach uses it to make changes in games from his sick bed in New York.
WhatsApp is, according to Ben Evans and many others, the biggest social network you've never heard of. It's a phenomenon - so much so that Facebook tried (and failed) to buy it in late 2012.
For the uninitiated, WhatsApp is an app that allows you to send free messages (text, images, audio and video) to anyone for free. It does for SMS and MMS messages what Skype did for voice calls. Unlike BBM, iMessage and others, it's no walled garden. It works across networks and across Blackberry, Windows Phone, iOS, Android, Symbian and others.
Its growth has been nothing short of spectacular. According to Onavo Insights, over a third of UK iPhone owners have it on their device. In Spain, that number is a staggering 97%.
In developing markets, it's no less impressive. I'm in Saudi Arabia this week on business. On my Saudia flight over, I noticed at least a dozen people using the company's distinctive UI. Our taxi driver spent an inordinate amount of time chatting to his friends on the app while driving us, at speed, to our hotel at 2am. Executives - young and old - are rarely separated from it for long. When I tweeted about WhatApp's prevalence early on Saturday morning, I had replies from India, Indonesia, Senegal and elsewhere - all saying they were observing the same pattern.
It's not just developing markets - its demographics do not easily fit the mould of early adopters. My mum uses WhatsApp. She's been using it for three years now. By comparison, she only discovered Facebook relatively recently. Friends and colleagues report having the same experience. People who never engaged with social networks are taking to WhatsApp, WeChat and other mobile chat and messaging services in their droves.
Perhaps one of the most striking features of WhatsApp is that, unlike other social networks, the users are not the product for sale. The company's founders are vehemently opposed to the idea of introducing any type of advertising onto the platform. You pay to use WhatsApp.
The company announced a standardization of its pricing across all platforms this weekend. Previously iPhone, iPad and iPod Touch users had to pay a one off fee £0.69 up front where Android users got it for free for a year before a £0.69 per year subscription fee kicked in. Now everything works the same - one year free and an annual £0.69 subscription from then on. The initial free year on iOS is likely to result in a slew of new users finding the platform for the first time - free apps tend to get 10x or more downloads when compared to even the cheapest paid apps, so expect that 200 to 300 million users figure to creep upwards quickly over the coming months.
More users equals more potential revenue - so it came as no great surprise when rumours began to spread around a possible move into WhatsApp gaming this weekend. Though the site that originated the story has since moved to correct it, there's no doubt that such a move has already paid off for their competitors. Kakao Talk, a similar Korean app generated 82 million game downloads from 23 milion users over a three month period in 2011 - generating $51.6 million in the process. Similarly, Line, a Japanese messaging app has had well over 100 million game downloads since they launched their service in July 2012, with one game alone generating $1m in revenues in just 12 days.
Those numbers are hard to ignore for a company with an investor like Sequoia on board. Numbers like that move companies towards IPOs or Instagram-style 10-figure exits. With that said, WhatsApp's CEO, Jan Koum said in a rare interview this week "We don't have an exit strategy because we don't plan or want to think about it. We want to focus on good products."
Regardless of their lack of desire when it comes to discussing these rumours, we can expect to see them surfacing a lot more frequently over the coming months. In the same way that Instagram posed a threat to Facebook as it started to encroach on the photo-sharing functionality that was one of the key drivers of their success, WhatsApp poses a clear and present danger to Facebook, Twitter and many others.
For Facebook and Twitter, it's a threat as it provides an outlet for people to chat and share information with their friends in a way that's far more segmented and private than either of their networks. For Google, it is a potential money making machine which handles over 10 billion messages a day - all containing content which they can't access. For telcos, it's a pain and it's a partner. All are potential acquirers, as is Microsoft - who must look at charts like this (where blue represents searches for WhatsApp and red represents searches for Skype on Google) and worry.
Right now, it'a also difficult to rule out Yahoo - who, under Marissa Mayer, are taking a long hard look at mobile opportunities in the market.
My guess - it's either an IPO or Microsoft acquisition. WhatsApp's founders both came from Yahoo, so they've been down the big company road before. Their stated disdain for ads is a pretty big indicator for me. If they were to go with Google, Facebook, Yahoo or Twitter, it would be hard to avoid the eventual appearance of display ads within the app. While there are operators who could buy them out, I'd imagine the founders would balk at the restrictions that would gradually be imposed by that type of relationship. Microsoft has the financial clout to make an acquisition happen, and the amalgamation of WhatsApp and Skype would be interesting as well as a huge potential revenue centre for Microsoft.
I must admit, I'm leaning towards an IPO. The money raised would allow WhatsApp to buy or simply build a VOIP service at some point in the future. It would allow them to stay far more independent and pursue their own plans and ambitions. The risk is, as with every platform, a competitor could overtake them. Of the many ways to mitigate against that, WhatsApp's simplicity might be its saving grace and its greatest asset. Watch this space over the next 12 months, as this sector is about to get very, very interesting indeed.