This is a sneaky one.
This involves establishing a bluetooth paring with another phone.
Once the other phone accepst the paring, a "back door" is establish.
That means a connection remains and the owner of the phone being snarfed doesn't know that his information is being accessed.
That means you can literally transfer all the files, phonebook etc, or use any services of the victims phone.
The catch is, if someone is willing to pair with you in the first place, it is likely to be someone you know.
So be Careful when you pair with your friend in the future.