There's actually a bit of a trick to making that happen. You will want to go into any contact, and open the SMS messenger. From there, you can craft your message with text and emoticons (images), then simply copy everything and paste into your template.
You can also copy and paste an existing template into this same SMS messenger area, and modify it to make editing much faster.
To open the emoticon popup...simply click on the smiley face icon (circled in RED INK):