At fault or negligent for accident while using cellphone in MA?

No, there is no hard and fast rule or law that creates fault or liability based solely on the fact that one party was using her cell phone.  After all, it is not illegal in Massachusetts for adults (over 18) to drive while using a cell phone.  The issue of whether you were at fault in an accident or negligent (and thus liable to pay damages to another) will depend on the facts of the incident. 

However, it is certainly possible that your use of a cell phone during an accident could increase the changes of you being found negligent or liable for damages by a court.  For example, in a situation where a fact finder is attempting to apportion the blame of the parties, say in a case where a pedestrian jay-walked and was hit by a car, cell phone use could certainly be a large factor in shifting the blame to the driver.  If the driver is paying attention, two hands on the wheel, and a pedestrian steps in front of her car outside of a cross-walk, then it seems like the pedestrian is more at fault.  But what if the driver is using his cell phone and not paying attention?  Then, perhaps, both parties share some of the fault, and the likelihood that the driver will have to pay some damages increases.  Under the Massachusetts modified 'comparative negligence' system, a defendant can collect for their damages even if they were also negligent.  Hope that helps.