Working adults, especially knowledge workers, like to brag (or is it complain?) that they are "multitaskers." These individuals no doubt comprise a very vibrant part of the economy, but this sort of armchair psychology is baseless, and, when applied to domains such as driving while speaking on a cell phone, potentially dangerous.
In research on multiple task processing reported by Time (more fully published in Psychonomic Bulletin and Review), the expected result based on previous studies, was borne out: "During the hour-and-a-half session, 97.5% of the students [subjects] showed a significant decrease in their driving abilities and memory skills while multitasking." Other research had shown that people can alternate between tasks, but are generally not able to perform demanding tasks concurrently. What got the broad press interest was J. Watson and D. Strayer's finding that around 2.5% of the subjects showed no such decline, and a few "supertaskers" actually did better.
By all means, let's have DARPA build cyborgs that exploit the capabilities of supertaskers. Public policy restricting calls to hands-free operation miss the point and do not address the underlying performance deficit suffered by most drivers. Consider the summary offered by Science News:
As expected, overall group performance declined markedly when driving and the cell-phone task were performed at the same time. Volunteers took an average of 20 percent longer to hit the brakes when needed, and increasingly fell behind the pace car.