Facebook is testing charging you to send messages to non-friends
Say you went and saw someone speak at an event and you want to Facebook message them. If you're not Friends with them, your message will go on to the "other" tab and might never be seen by them. Facebook thinks they can change that for $1.
Facebook thinks charging for messages will cut down on spammers and ensure that only messages that need to get there will get there. If you pay the fee, your message goes into the Inbox, instead of the little-known other folder.