Is talking on the cell phone worse than just talking to a passenger?

According to the study (which used 41 drivers), talking on the phone made a significant impact on driving, causing them to drift lanes, miss exits, and just generally drive like the jerks that make you yell “GET OFF THE FREAKING PHONE!” to people in front of you in traffic–even without having a phone in their hands. Meanwhile, talking to a passenger in the car had little or no impact.