Harnessing Bluetooth Viruses for Messaging
A Bluetooth messaging client could allow phones and other devices to bypass other networks to receive "broadcast" messages and data, but for security's sake, it could only be done in highly controlled environments such as schools and businesses. The code would also have to use some kind of certificate or public-private authetication key to ensure that a sent message stayed within the clearly defined group of recipients. People wanting to participate in "flash mobs" might want to play with this, but it could have other applications -- entertainment, education and even marketing are just a few applications. But again, the security issues inherent in making Bluetooth "discoverable" need to be addressed first.
Sources: The Mobile Technology Weblog, Smart Mobs