Cell phones can certainly be problematic. One example that happened with me went like this: The strong A student finished an exam and left. Shortly thereafter, her friend, a very weak student, got a phone call and walked out to take it.
When I followed the second student out and asked her if she was done with the exam. She hung up with a frustrated expression and started back to class. Just then, her friend walked out of the restroom putting away her own cell phone.
It is not practical or desireable to confuscate an adult's cell phone and investigate the call or text history. So rather than accuse students of cheating with their subsequent denials and defensive arguments, I simply explain that their actions give the appearance of cheating and it would be a shame for them to be dropped because of that. They get the message and I don't have to fence with bogus denials.
