If you know what wii speak is, just scroll to the bottom of the message and read the bolded.
I'm going to assume that you don't know what it is. This is wii speak and where it is put when it is setup.

It connects to the Wii via USB. It's a mic, etc.
Now for how it is used for the game.
As far as we know, we can only talk to friends that we have added via friend code/wii code and to the friends on those friends friend list in private games.
Basically, yes. You talk, the mic picks it up and your friends can hear you. Either to be used on the Wii Speak Channel, Animal Crossing or The Conduit when it releases.