Yesterday, Facebook released an app dedicated to messaging for iOS and Android. The free app, which quickly shot to the top of the list of free downloads on iTunes, lets you communicate with friends in real time through either Facebook chat (instant messaging over WiFi, 3G, 4G) or via SMS text messages.

Facebook has said that the reason it put out a separate app for its messaging is to make it faster. You still converse with Facebook friends in the main Facebook app—the new app is just faster and includes the option to send a text.

The app seems most similar (and perhaps competitive with) BlackBerry Messenger, which allows messaging between BlackBerry users. It also may be worth pointing out that when you download the Android version of Google+, one of Facebook's biggest competitors, it actually generates two distinct apps: one for the social network, and another for Huddle, its messaging component. So Google+ has a dedicated messaging app (on Android anyway), perhaps also for performance reasons.

SMS Texts and Instant Messages
As with many Facebook services, the app isn't wholly innovative—others have combined SMS with instant messaging before—but what makes it special for most users is that it leverages their Facebook networks. One of the often-overlooked strengths of Facebook is that it's a central source of data about your friends, including their phone numbers, email addresses, and whereabouts. If you want to send a text message to a friend but don't have her phone number stored in your phone, you can quickly send her a Facebook message instead. And if she's added her phone number to Facebook and granted the appropriate permissions, the app will automatically pull up her number as an option, in case you would prefer to send her a text.

One minor glitch I found is that when I sent messages via SMS to my friends' phones, their Facebook profile pictures didn't turn up. Instead, I saw the stand-in blue and white silhouette. When I sent messages via Facebook chat, each person's profile picture did appear next to the conversation.

Push Notifications and Location Services 
One feature I especially liked in the Facebook Messenger iPhone app was the ability to not only turn on push notifications (those alerts that ding and wake up your phone's screen when you receive an incoming message), but turn them off for a select amount of time. You can choose to keep push notifications on permanently, or switch them off for one hour, or turn them off until 8am the following day, if you want some peace and quiet overnight.

Even better, you can turn the alerts on, off, off for an hour, or off overnight for each conversation. If you're caught up in an important discussion with one group of friends and need to temporarily silence another conversation that's less important, you can. A cog icon for these settings appears at the top right of every dialogue history, so the controls are always within easy reach.

The new app has location services, too, which you can enable or disable with each new message thread in which you participate. An arrowhead icon lives at the far right of the text entry box. When it's blue, location information is shared. Tap it once to turn it gray, meaning your location will be kept private.

Do You Need TWO Facebook Apps? 
If you spend a lot of time communicating with friends from your mobile device, the Facebook Messenger app is worth downloading. I personally like compartmentalizing certain aspects of social networking, so I like the idea of having instant messages and Facebook text messages in their own area, cordoned off from status updates, photos, and all the commenting that comes with them. If you prefer a one-stop-shop for everything Facebook has to offer, the only things you're giving up in not downloading the new app are 1) the ability to find more people's mobile phone numbers and 2) speed.