Its part of the bluetooth protocol defining the device class and profile, available in the discovery process. Nothing to do with mac address, frequency etc which are at a completely different layer. What you may be talking about is the difference between a Headset profile and a Hands-free profile.
Have a look here:
http://doc.trolltech.com/qtopia4.2/qbluetooth.html and this tool is also quite useful:
http://bluetooth-pentest.narod.ru/so...generator.html