bluetooth headsets; They CAN listen if they want.

Security is inversely proportional to usability. Using a bluetooth headset with your cell phone is easy to set up and use. Most devices use the password 0000. When you forget your password it isn't hard to find out what it is by doing a google search.

If it is easy for the non-technical person to setup their phone is it child's play for a professional to take advantage of the situation.