In iOS of iPhone Emoji keyboard is installed by default. User is required to activate/ enable this feature in the smart phone. But for latest iOS5.0.1 following steps are required to be taken for enabling.
First of all Launch Settings from the menu and tap on “General”
Tapping any Emoji icon enters it into a text field as if it were a standard character.
Tap on “Keyboard” and then again on “Add New Keyboard”
Scroll down the alphabetical list to “Emoji” and select on it to appear in your list of active keyboards
Now Close the page and leave out of Settings
Enter into any text entry location: Messages, Notes, Mail, etc
Tap on the globe icon next to the Spacebar button to access the newly enabled Emoji keyboard
Individuals who are using iOS5 can use Emoji keyboard only if he first enable it from the settings. One more thing to share is that Emoji graphical icons also support OS X Lion .So if you are writing a message to a person who is using Mac he can also see the icons in the message.