According to a study conducted by Carnegie Mellon and the London School of Economics, talking on a cell phone while driving "may be distracting, but it does not lead to higher crash risk." The scientists conducted the study between 2002 and 2005, examining call volumes during the hours that most carriers offer "free minutes", and compared that to data from eight million crashes in nine states. They found that though the call volume increased during these hours, there was not an increase in car crashes. They also found that banning cellphone use was not effective in decreasing crash rates.
This study suggests that drivers pay more attention while physically holding a phone to their ear and often slow down, but it also assumes that most people are driving during these peak call volume hours, which may not be the case. What about rush hour crashes caused by cell phone use? It also only focused on drivers who were talking on their phones, not those who were texting or using other features like the Internet. Only 11 states currently have laws against holding cellphones while driving. According to this study, those states have some thinking to do.