Roger Staubach told the story in his book of one day either he or someone else (I don't recall) was on the phone with Walt, who was in a pay phone booth. Walt needed to write a number or something else down.
"Got a pen," the caller asked Walt?
"Nope," Walt said, "but I got a knife. I'll just carve it into the booth here."
Classic. Staubach said he was quite a character.