WhatsApp, one of the most loved cross-platform messaging services, has reached a real milestone, with the news that its collection of apps are sending 1 billion messages per day.

Covering iOS, Android, and just about every other mobile platform out there, WhatsApp has one massive advantage over the likes of BlackBerry Messenger and iMessage, and that’s its cross-platform roots…

Sending almost 700,000 messages each and every minute is no small feat, and just goes to show how consumers are desperate to avoid SMS charges in countries where fees are disproportionate to the amount of data used.

“The mobile messaging market is moving, choices around platforms and their pricing and how they provide an amazing customer experience are the hot topics at hand. As a leader in the messaging space and with our network now handling over one billion messages a day, we see that the power is with the consumer.”

The astounding take-up is just another sign of the considerable mountain Apple’s iMessage has to climb. With existing iOS users clearly ensconced in the world of WhatsApp and other similar services, what do they have to gain from dropping it in favor of iMessage? On the contrary, the fact that iMessage is by design an iOS-only service could perhaps push people the opposite way until, one glorious day, we’re all iPhone owners.

Of course, as I’ve written about before, there could already be a real contender for the messaging crown in the guise of Google’s Gtalk system.

Do you use a third-party app to keep in touch with your friends via text, or are you falling in love with Apple’s iMessage?