A study published by Suzanne McEvoy in the British Medical Journal concludes that drivers who use hands free cell phones are equally likely to get into car accidents as are drivers who do not. According to a CBSNews.com report about the study, the "researchers used cell phone records to compare phone use within 10 minutes before an actual crash with cell use by the same driver during the previous week." According to the abstract of the report, "Driver's use of a mobile phone up to 10 minutes before a crash was associated with a fourfold increased likelihood of crashing." The abstact goes onto say that the "risk was raised irrespective of whether or not a hands-free device was used" and that the increased risk was similar in men and women and was not age specific.
While it's an assumption, my guess is that the study's 10 minute window was undoubtedly selected to account for any innaccuracies in the reporting of an accident's exact time. If that's the case, then one premise of the findings is that drivers who were on the phone at any time within 10 minutes of the reported time of an accident were also on the phone at the time of the accident. What the study doesn't tell us however is whether or not some other factor played a role in the accident. For example, were the cell phone users doing something else related to their phone usage that might have further distracted them. Have you ever pulled out a pen and paper while driving with the cell phone to your ear to write down a phone number and then noticed that your car was weaving? Guilty. How about looking down at the phone to find the tiny little "end call button" to terminate a call or the "answer" or "send" buttons to take a call that beeps through on call waiting. Just look at how small those buttons are on the BlackBerry 7100s (see How to pick a BlackBerry).