answer:There are a number of forums out there where people try to answer this question. This one says that the answer is that it varies. It depends on how many people are using the cell phone tower. More people, and they install a tower with lower wattage so it doesn’t go as far. Also, the more people who use a cell phone tower, the lower its range. I imagine that airports are probably particularly filled with cell phone traffic. The maximum range in the US for a CDMA tower is 38 miles. It’s 15 miles for GSM. That requires a tall tower in the mountains and more powerful equipment (in terms of wattage). Anyway, the answer to you question depends on your carrier and the strength of the towers and how many people are using the towers, and probably more. I can’t tell you a specific altitude.