It was probably a time of above-average communication -- and the messages were with a woman of above-average beauty and conversational smarts, so I had my reasons -- but it is still a useful window into how instant messaging sits right at the heart of the battle for attention that now dominates the technology industry. Skimming over those messages -- from the breezy rituals of good mornings and how are yous to hour-long heart-to-hearts -- shows how our phones are still fundamentally communicators, and how chatting, like everything else, is now facilitated by apps.

I was living in Dubai when those 5,600 messages were exchanged, and one of WhatsApp's most notable traits is that it seems to be significantly more popular outside the U.S. than it is within - almost all of my phone book's contacts in Europe, the Middle East or Australia are active on WhatsApp, while the ratio is much lower here in America.

At its core, WhatsApp is just a nicely-done messaging app that lets you send text, pictures and video to your friends anywhere, free. Unlike Apple's iMessage, it works on all the major mobile operating systems; unlike the text messaging services offered by mobile network operators, it doesn't charge you anything for sending the messages, and it works like modern mobile software, not the primitive SMS applications on most phones.

The problems WhatsApp solves could, in part, also explain why it is less of a big deal at home in the U.S. Most monthly mobile plans here include unlimited text messaging, creating an all-you-can-eat mentality around sending SMS that didn't exist overseas, where operators often charged per message. And while 310 million Americans share a single nation -- and telephone network -- in the rest of the world national boundaries between people are more likely to introduce the expensive headache of international calling and text messaging. That's another problem solved by WhatsApp.

But ultimately, the appeal of mobile messaging software is the same as the appeal of everything else on a mobile: it's with you all the time, it's always connected, and it has an immediacy that can't be matched. When friends are on WhatsApp, or iMessage, or BlackBerry Messenger, it's like you've opened up an endless two-way chat room.

And once it's open, the marginal cost of sending one more message, or sharing one more picture, is so close to zero that before you know it, you've sent a few thousand of them, in a few months, to a beautiful women a couple of thousand miles away.

The centrality of instant messaging to our mobile lives can be seen in how the giants of the industry have approached it. Apple's iOS and Google's Android have both built messaging applications that erase the distinctions between SMS messages sent over the mobile network and web-based instant messages, pushing users into their own messaging platforms in the process. BlackBerry has long highlighted it's BlackBerry Messenger service -- another mobile messaging product wildly popular abroad -- as one of its trophy assets.

Facebook added instant messaging to its Instagram photo sharing service, tried without success to buy messaging service Snapchat, and has now spent as much money buying WhatsApp as the market value of American corporate giants like Gap, Blackstone or Harley Davidson.

Is the valuation worth it? I have no idea, but I do know this: last week, after a years of constant usage and tens of thousands of messages, WhatsApp told me my free trial period was coming to an end, and I needed to cough up a dollar for another year of service. I paid it without second thought, and I'll bet a large majority of the company's 450 million active users will do the same.