Up to four people from your household can live and work together to build the perfect town. Design clothes and patterns, write letters and post messages on the bulletin board for each other, or invite up to three friends to visit your town using Nintendo Wi-Fi Connection. With the new WiiSpeak microphone, it’s like you’re all in the same room. The microphone sits atop the sensor bar and picks up the conversation of everyone in the room to encourage a more inclusive experience.
So far the microphone has only been linked with Animal Crossing, we'd expect other games to make use of it in the future but for now just that game is mentioned.
From the pictures provided it looks like the microphone will connect to the USB port at the back of the console, this will allow the microphone to connect to the Wii and draw power at the same time like any other USB device.
Because of this, we'd pretty much expect to find the microphone bundled in with the game when it goes on release in North America this Christmas. No European release date has yet to be set but shouldn't be too long after the American release.