its not as plug and play as xbox voicechat is (which ive never used but hear works well) but there is an easy way to of course do voicechat with mario kart.
it does require a bit of PC knowledge and is only really for your friends.
Simply setup skype/teamspeak/ventrilo or any other voice chat software on your computer or laptop and buy some headphones with an integrated microphones.
thats it. works an absolute treat and as fun as mario kart is i cant stress how much more fun it is playing with your mates and being able to talk, laugh, swear, whatever at them. makes a huge difference imo.
as im a bit of a computer geek this is particularly easy for me to do as i run the wii from the computer monitor so everything is right on hand. for your normal people who have the wii in the front room and dont have a hulking pc right next to it or a laptop you can use then i guess it wont be quite as simple.
but if you have a laptop, headset and skype then its a piece of badger pie to sort out
