You don't need this app if you know how to replace the font manually. Please follow the instruction in Emoji Keyboardhttps://play.google.com/store/apps/details?id=com.klncity1.emojikeyboard

If you don't want to think too much, you can download this app to help on replacing the system font easily.

Function:-Support ios5's emoji (black & white only)-Download Emoji font from internet-Backup system font to SD Card-Replace & set the permission of the Emoji font-Restore the original system font from the previous backup if you like.-Rename DroidIndia.ttf which can solve some of the encoding function (the button will only show up if your phone has this font)-Delete all the downloaded & backuped files in SD.

If you want to input emoji, you can try to use the below apphttps://play.google.com/store/apps/details?id=com.klncity1.emojikeyboard