The Emoji keyboard is build-in in iOS.
The only thing all the "Emoji" apps existing on the AppStore (like "emoji-free!") are doing, is that they activate this keyboard in the System Preferences, because it is hidden by default.
These apps don't "create and install" the keyboard itself neither do they install the icons and glyphs (symbols), the smileys are already built-in in iOS too.
For example if an iPhone user receive a text message (SMS) containing some smileys, they do will see the smiley, even if they don't have installed any "Emoji-enabler" app like "Emoji-free!".
To be more precise, the emoji icons that Apple embedded in the iPhone fonts are not approved by the Unicode Standard. They are located in the "private" plane of Unicode: their codepoint is in a range that is especially reserved for private uses -- like the one Apple does by using it for these emojis -- but by definition as it is a private region, there is no dedicated name and standardized usage of these codepoint accross applications (contrary to codepoints like U+0041 which is dedicated to the glyph representing the latin letter "A")
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