Don't you just looooove techno savvy teachers?!?! I used to do a secret code during Calendar Time (idea from the book The Calendar and Beyond by Kimberly Jordano). This is a fantastic book with TONS of ideas. Go get it, then come back. :)
I like this version of the activity because you get more bang for your buck!
Mrs. I's Class: Phone Secret Code (freebie): "Here is another word work activity that I put together. I used the keypad (found in the printable) and glued it to construction paper. The..."