Facebook Messenger is an app, completely separate from the flagship Facebook app, which lets you access your chat with your Facebook friends from a streamlined interface on your mobile device. In addition, the app can integrate with SMS for a completely unified text-and-Facebook chat experience. And for those who prefer to keep Facebook correspondence separate from text messages, the app makes it easy to maintain the divide as well.
For anyone familiar with Facebook chat on a desktop browser, the Facebook Messenger mobile app should feel completely familiar. It lets you send messages to one or more recipients, as well as reply with text, photo attachments (from the Web or from your mobile device), or voice recordings. There's also a menu to add Facebook emoji to your conversations.
The latest update to Facebook Messenger added a hugely convenient VoIP calling feature for users in select countries, including the U.S. and Canada. To use it, just go to the Info page of any of your contacts and tap Free Call. It's really simple, and the feature works like a charm. And of course, your carrier minutes will not be used, but normal data charges will apply. If you want to make a normal voice call using carrier minutes, you'll have to leave the Messenger app in order to do so, which is a bummer. It would be great to get the option to place either a carrier call or VoIP call right from the app interface. Also, video calling would be a welcome addition, considering the feature is already available through your desktop browser.
Another thing I'd love to see is the ability to switch between SMS and Facebook chat in the middle of a conversation. This would allow you to take advantage of Facebook when the person you're contacting is online, then switch to SMS otherwise. For now, the app keeps text messages and Facebook conversations separate, even if they are with the same contact, whereas a more integrated approach similar to that of Apple's iMessage would make a lot more sense.