You can see when phones are turned to airplane mode and are not using cellular data. Neither were on airplane mode. While it's nice of you to assume they were using wifi, you're wrong in this instance. I had a very clear view, especially of the first guy. He was making phone calls with the iPhone's default phone app, no airplane mode, while the plane was racing down the runway and during lift off. I found the whole thing to be very strange and watched closely because he kept trying to call the same contact over and over repeatedly (a guy in his phone named Yousef something) and the guy never answered.