Driving + Cel phone = Drinking + Driving?

According to an article in Globe and Mail, talking on a cel phone while driving has the same effect on attention level and reaction time as drinking (to the legal limit) and driving. The really interesting part is that it doesn't matter if you are clutching your handset or on handsfree. So how do the numbers compare to chatting with a passenger? Why is it so different?

Read the article

Update: So talking on the phone is one thing. But texting while driving is a whole other thing. Current news reports are claiming that the engineer who ran the rail signal and caused the LA train accident might have been text messaging at the time. 26 people died. Really, there are no words.