Caller ID is a pretty limited thing, with unknown numbers just showing on screen as a bunch of numbers. You really have no idea who's calling, but Facebook wants to change that.
With their Hello app, you log into your Facebook account and then use it as a dialler. When someone calls you, you'll see some of the information they share publically on Facebook, so you'll get a brief look at what they do and possibly even their age, as well as whatever their latest profile picture is. Here's how it works.
It's a slightly different spin on called-ID which Facebook will be hoping to make popular and keep you inside their software loop for even longer. It expands upon services like WhatsApp by offering voice calls and text messages but also giving you additional information, which extends to contacting businesses. In short, it's a neat idea which might actually manage to take off - we're just hoping Facebook doens't infest it with ads in the future.
The app is currently on the Google Play Store here but you can only download it in the USA, Nigeria and Brazil for the moment. It also seems like this functionality is only set for Android, likely because of the stricter guidelines for apps and access on iOS. More as we get it.