At this time, we do not have emoticons built in to WhatsApp for iPhone. However, emoticon support is built into every iPhone by using the "Emoji" keyboard. If you are using iOS version 5 or higher, instructions for enabling emoji can be found here .
Once the Emoji keyboard is enabled you can access it here:
Please note that iOS 6 has introduced additional emoji characters. In order to send and receive all of the new emoji characters, you will need to have upgraded your iPhone's software to iOS 6 or later. Instructions for upgrading your phone's software can be found here.