This.
A typical cell-phone has a range of 2-3 miles. The reason they are called "cellular" is because they operate inside a "cell" of a certain electronic boundary. I found when working for an air-ambulance company that the cell-phones for the ambulance would lose coverage at about 150-160 knots on takeoff or landing.
The explanation given to me (which makes sense) is at that speed, the time time spent in a particular "Cell" was insufficient for the towers defining that cell to establish a connection. Just as it was establishing the connection on a specific frequency, it would lose coverage, and the process would start all over.
I also believe the tower propagation patterns are optimized for horizontal coverage, not vertical.
There may be exceptions in the states, where tower density is high. But certainly not over the open ocean, in Asia.