Until now, using emoji in parts of Android besides Hangouts could be a little tricky. Officially, the emoji keyboard was included as part of the iWnn IME, and required users to manually switch using the persistent keyboard notification which appeared any time a user tapped a text field. Even then, users couldn't enjoy the full-color emoji found in Hangouts. This was certainly less than ideal.
Thankfully, Google has spread "Emoji everywhere" with Android 4.4 KitKat, integrating the set of awesome emoji with Google Keyboard for easier access.