You can easily enable emoticons on your iPhone if it is running iOS4.0 or later. Apple has made it very much easier to do this. Here are the steps:
Step 1: On your iPhone, go to Settings
Step 2: Select General >> Keyboard >> International Keyboards
Step 3: Now select Add New Keyboard
Step 4: Finally select "Emoji"
Step 5: Reboot/Restart your iPhone
Now will see a little globe icon near the space bar. Just select the globe icon and you will see your iPhone smileys/emoticons.