NJ was among many states that considered using a cell phone without a hands-free device a secondary offense. (You wouldn’t be pulled over just for that.) But as of March 1, 2008, New Jersey has changed the law so that using a cell phone without a hands-free device is a primary offense - you can be stopped just for that.
NJ joins California, Connecticut, New York, and Washington. In NJ, it’s a $100 ticket.