There had been rumors that Facebook was planning to get into the email scene, but it turns out that this was just a side effect of its latest move - a single, unified messaging interface for all the ways that its users can contact their friends, including IM, email and SMS. Of course, Facebook would like nothing better that every message you send, regardless of the medium, will be through its servers.
Wired - Facebook is seeking to replace e-mail with what it calls a “modern messaging system” that combines all the ways people send messages — including e-mail, IM and SMS — into a single interface. It’s a clear assault on Google and and its popular “social” application — Gmail. The new system, Facebook Messages, was announced Monday. It allows you to simply click on a friend’s face, type a message and hit Enter. Facebook handles the rest. And it comes with an optional “facebook.com” e-mail address.
It remains to be seen how good the system is able to decide which medium you're currently using and route the messages timely, probably by detecting where and how you're logged into Facebook, but if you want more details, click here.