Emoji are cute little Japanese icons that can be sent in SMS text messages. They will appear to the receiver of the message if their phone is an iPhone with 2.2 software, or if their phone has support for emoji.
Up to this point, only users in Japan had access to them on the iPhone (that is, if you didn't want to hack your iPhone). Now, if you download a $0.99 app called frostyplace, you too can add emoji to your iPhone. Here are step-by-step instructions: