Interesting. My logic says that nearby cell towers would cause more interference (during take-off / landing), because the tower is sending much stronger signal

Interesting. My logic says that nearby cell towers would cause more interference (during take-off / landing), because the tower is sending much stronger signal than a phone. (A tower with high gain antenna can easily pick up a weak signal from a phone, while the phone needs relatively strong signal for its low gain antenna. Or maybe the phone signal is still stronger in the plane due to the inverse-square law?). Then again, I'm not an EE.