I'm going to make a prediction about Facebook's mobile event tomorrow. I'm probably wrong, but I have reason to believe that Facebook is going to announce some type of facebook chat feature that allows you to voice chat/call people that are online on fb. As long as they have the proper hardware of course.
My ONLY reason I think it's a calling thing is because in their invitation picture, it looks like the two people in the middle are using the old tin cans and string trick to talk to eachother from far away. Look:
What is Facebook about to unveil? | Android Central
I'm guessing it has something to do with calling people, voice chatting, etc. We'll see tomorrow. Whatever it is, I hope it is compatible with my Droid 2.