The guestbar over on Boing Boing has a great little bit on emoji.

Since i-mode was first introduced in Japan, mobile phone users there have used text emoticons called emoji to send dense messages in fewer bytes. Top providers DoCoMo, J-Phone and AU/KDDI have begun offering proprietary sets of emoji characters enabling two users on the same service to send messages to one another on the go without conventional text.

(Unfortunately there's no way to link to the guestbar articles.)