Mario Kart Wii doesn't have voice chat. But it's got text chat at least, right? No. It doesn't even have that. Nintendo of America have announced that the game will instead allow players to choose from a limited selection of automated statements/responses while playing the game. "Hello", "I'm sad", etc. I'd say welcome to 1996, Nintendo, but 1996 is still awaiting your arrival.
Mario Kart Wii Text Chat Details [IGN]