Loopfuzz - Sorry, I don't have any link to this, just an explanation.
Below is an excerpt from someone else who wrote on this subject - I thought it made sense from what I know about the Aircell system.
"To understand why you have the 10,000ft limitation, you have to go back
to the days when AirCell first came on the market.
The original concept was that there was an existing network of cell towers across the U.S. Those towers were vertically polarized, which means that the radio signals were transmitted horizontally. The inventers of AirCell found that they could mount horizontally polarized (vertically transmitting) antennas on top of the existing cell towers without causing interference with the ground based cell service.
A long legal battle which included hours of testing ensued. The end result was that AirCell was able to prove their theory and was granted FCC rights to transmit vertically. Of course the next steps included making binding business agreements with the cell tower's owners. These agreements, obvious, had to include language that would provide assurance that there would not be interference with ground cell ops, but also that there would not be competitive services offered.
That's the background. This is why the FMS or altimeter must validate
that the aircraft is above (I'll come back to word "above" later) 10,000 ft
. You can see why a gear up switch would not meet that requirement. This
ensures that the transmissions are taking place on the horizontally polarized antennas and not on the vertically polarized antennas. If you check your documentation closely, you'll see that the connection level is listed at above 10,000, not at 10,000 feet. While it is true that the system will connect "at" 10,000 feet, the assumption is that the aircraft will be in a climb condition at the time of acquisition. Also, keeping in mind the tolerance of the altimeter accuracy, it is imperative that there be a small window to ensure that the 10,000 feet limit is reached."
