Consumer grade GPS chips are designed to quit working when they sense they are traveling above a certain speed and/or altitude. This is for security reasons (think missiles). I used to work at a GPS company. We had an entire Military division that had products controlled by the Dept. of State and Dept. of Commerce for this very reason.
This is not true at all. It may have been, years ago, but not anymore. Consumer grade GPS chips as found in cell phones most certainly do work at typical aircraft cruising altitudes, it's just sometimes hard to get a signal as they usually depend on approximate location data from the mobile network and then determine the more accurate position from that.
I've been able to get an accurate GPS position at 35-40k ft on a Blackberry, various iPhone and iPads, and Android devices, in many parts of the world, including over the middle of the Pacific and Atlantic.
The deliberate error introduced into consumer-grade GPS devicesby the US govt was removed years ago.