There are so many types of free smilies available. First I have installed free and best smilies from Internet in my mobile. I am using smilies in Email by pressing symbols of smiles on twice from the menu bar.
I don't think you can in the Messages app. If you really need smilies, you can sideload and setup Aico Mail, an android mail app. It has a bunch of smiley inserts (frowns too)