The Nintendo Wii is currently the only gaming system unable to give players the ability to voice chat over the internet. Though a few games have been released on the Wii featuring online play, none allow players to converse through them. It's a frustrating limitation.
During a question and answer session in a Nintendo conference call this morning, Reggie Fils-Aime addressed this issue.
According to Fils-Aime, the system is clearly capable of this function, and Nintendo is constantly adding and tweaking features of the Wii system through system updates. The issue boils down to locking down the specific technologies and getting the specific peripheral to allow voice chatting.