When you look at monthly active users, WhatsApp is streets ahead of the competition

WhatsApp, Telegram, LINE, BBM... there are many apps that regularly tell us how many users they have. We saw this yesterday with WhatsApp's announcement that they now have 500 million users. But these announcements don't always reflect the reality of how many people are actually using the apps.

Lots of people try out new apps, but few keep them for very long, especially if that app replicates another service, as with the communication apps above. Users download, install, test and then remove most apps.
LINE, for example claimed 300 million users at the end of 2013. But as the Wall Street Journal writes, when you look at monthly active users, that figure is 175 million, while WhatsApp claims 465 million active users. Similarly, Viber had 200 million users in May 2013, but only half of those are active.
It's important to note the difference between users and active users, because so many of us sign up to free services to try them out, and then don't user them. What the current data shows is that WhatsApp is really well established, with a high percentage of active users, whereas much of the competition is actually struggling to keep users active after they sign up.