BBM might be getting the headlines right now (not necessarily good ones either), but Facebook hopes to challenge it for the frontpages with the launch of Facebook Messenger.According to the Guardian, this standalone app has launched for iPhone and Android handsets, with that cross-platform nature likely to make it a real rival for BBM and Apple's iMessage. Essentially, it ties into the existing Facebook Messages feature on its website, which pulls together texts, chats, emails and instant messages, also allowing you to send messages to Facebook friends or other people in your phone address book, delivering them by notification or text.Facebook engineer Lucy Zhang wrote: 'More and more of us rely on our phones to send and receive messages. But it isn't always easy to know the best way to reach someone on their phone. Should you send an email or text? Which will they check first? Did they even get your last message? We think messaging should be easier than that. You should be able to write a message, click 'Send' and know that you will reach the person right away.'The downside? The launch was in the US, with UK users forced to wait just a little longer. We suspect not too long though, as there's nothing here that's necessarily location-specific. As soon as it hits the UK app stores, we'll let you know.