Among educators, it is mostly an unwanted presence. Cellphones go off in class, disrupting lessons. Students leave classrooms to make calls in the hallways. Others play video games or watch movies that they have downloaded onto their laptops. Some students even use hand-held organizers and cellphone messaging to exchange answers and cheat during tests. The problem is more common in the higher grades, although some devices, particularly hand-held ones like Game Boys, have trickled into elementary schools.