If you have the default keyboard selected via Input Method when in your texting app, then long press on the 12!? button second from left bottom row which will bring up your page of smilies. When you press send message they should then appear in the sent message on your phone as the image not the text however it depends on what handset is receiving them whether they convert to an image or remain as text.
Works the same on the Android keyboard, altho the smilies are shown as text on the smiley button bottom right of keyboard but turn to an image when sent.
On both keyboards, having sent a smile from my X10 to my X8 the X8 receives as an image not text.