This little hack has been around for awhile but now you can do it from your BlackBerry. It involves simply telnet-ing to a HP LaserJet printers IP address on port 9100 and sending a specific command. That way you can get the printers LCD screen to show whatever text you want. This does not work on all LaserJet printers but since it is a free app it cant hurt to try. Keep in mind to not get fired by using this application if you have an overeager security department but it is great for a practical joke.
Image courtesy of Mbcharbonneau