A post in Bugtraq with link to the :
During the last year, rumours had come to my attention that apparently it is possible to transform a standard 30USD Bluetooth(r) dongle into a full-blown Bluetooth(r) sniffer. Thinking you absolutely need Hardware to be able to hop 79 channels 1600 times a second I was rather suspicious about these claims.
This paper is the result of my research in this area, answering the question whether it is possible or not..
Get it at http://www.remote-exploit.org/research/busting_bluetooth_myth.pdf