Most are set for 60k max, and some speed limitations also - this is an export requirement from the DOD...
The phone uses A-GPS, so sometimes if it loses the ground based assistance - which it will - it can get confused and not fix properly.
I don't know of a specific limitation by Motorola - but it would not surprise me, since most people don't use their phones at 20k feet - heck, some of us can't use them at 850 feet ASL... haha.
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