The Drs. Eide found a study showing what happens in the brain when driving and talking to someone else...not on a cell phone, but to someone else in the car. It turns out that this type of multi-tasking, just listening to another person while trying to drive, involves visual and spatial areas of the brain that are also needed for driving. In other words, listening robs attention and capacity from the parts of the brain required for safe and effective driving. Cell phone use while driving certainly does the same sort of thing, but we are just learning what happens physically in the brain that makes cell phone use so distracting and dangerous.
I should mention that I often, at stoplights, observe how many cars drive by with cell phones to the driver's ear. My record so far is seeing 8 cars in a row with drivers with a phone to the ear. The illusion for those individuals is that the cell phone conversation does not affect the driving, so there is no danger. We need to change this myth with the hard data and evidence of studies such as this to show multi-tasking is not as hardened as we want to believe.
I am looking forward to seeing additional studies related to classroom participation and learning while there are side conversations that disrupt other students.