Post office box keys double as letter openers

The Idea:  Design post office box keys so that they can also be used as a letter opener as well. 

The Background:  When I moved back out to Colorado since I am in a ski town there is not any residential mail delivery therefore I had to get a post office box.  So when I go to the post office now I often want to open at least a few of the items I have received.  However opening a letter with a key does not work as well as one of those smooth letter openers.  So I would love to see a key designed with a normal key design on one edge and a letter opener design on the other edge.