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A cell phone is simply a radio transmitter that tries to talk to any cell towers it can. When it's on the ground, that's about 3 or 4 cell towers with an active connection to you. When it is 100,000 ft up, your phone can transmit a several state radius (thousands of cell towers). Each tower will connect to your phone, potentially overwhelming the system. It's like yelling in your room versus yelling in a library, with a bullhorn. APRS is the way to go. It transmits at low power, once a minute, and the worst you can do is piss off the ham radio operators, not the national cell network.