If you're familiar with the Messaging app on Windows Phone, you may assume that the identically named Messaging app inis, well, identical. It's not quite the same, actually, and is more accurately described as a Metro-styled version of Windows Live Messenger, Microsoft's PC-based instant messaging application.
The biggest difference between the two mobile apps is that Messaging for Windows 8 does not support cellphone/smartphone services such as SMS and MMS, since these occur over carrier networks and almost always incur additional fees. Instead, Messaging works with Microsoft's Messenger network, of course, and with Facebook.
Like all Metro-style apps, Messaging provides a simple, full-screen interface. It consists of a threads pane for tracking the conversation threads you have with others, a messages pane that contains each of the conversations you've had in the currently-selected thread, and text box for adding comments to that thread. Messaging tracks the online status of each participant in a thread and supports multiple services, though again only Messenger and Facebook are currently available.
When you activate the Messaging app bar—by right-clicking a blank area of the screen, tapping WINKEY + Z, or swiping towards the center of the screen from the top or bottom edge—additional commands are revealed. These commands are largely obvious: Status (for settings your online status), Delete (which will delete the currently-selected thread), Switch (for changing manually between supported services), and New, for starting a new thread.
That last command is a bit interesting in that it provides a peek at a Metro interface I haven't covered yet, the People picker. Like the more commonly understood File picker, the People picker can aggregate content from multiple sources, though in the Consumer Preview, at least, only the People app's contact list is currently available.
The picker is also smart about which contacts to show you. That is, it doesn’t provide you with a rote list of every single contact you have. Instead, it only shows you those contacts that are connected to a compatible service and are currently online. It's not particularly smart about some things, however. You can't send offline messages to people with whom you don't already have an available thread. And I don't see a way to start a multi-contact conversation, let alone perform an audio or video chat. Currently, only text chats are available.
(As always, we must assume that many of the limitations we're currently seeing are related to the fact that these apps are in "App Preview" mode and are, thus, horribly incomplete.)
Unlike Calendar, the App Preview version of Messaging already supports notifications, which appear as floating "toasts" near the top right of the screen.
And Messaging actually works pretty well in snapped mode, as well, which certainly isn't the case with many Metro-styled apps.
Ultimately, what we're left with here is yet another incomplete but promising App Preview. Messaging offers the basics--text chat, support for the Messenger and Facebook services, and decent notification and snapped experiences. But there are many standard IM features missing here, and I'd be surprised if the final version didn't offer some Skype compatibility too. Stay tuned: This app will almost certainly be getting much better in the months ahead.