As for using a phone at cruise (35,000 feet), the cell tower signals DO NOT reach that high to even use your phone, although the phone still transmits a signal which causes the interference...
That is incorrect. All current cell phones (AMPS, GSM, CDMA, iDEN, "TDMA" (IS
-54/136), etc...) wait until they lock onto a signal from a tower before powering up their transmitters.
There are several reasons for this mode of operation. For one thing, a multiband phone doesn't know which band(s) are in use in the regulatory zone in which the phone is located. By waiting to receive a signal before transmitting, the phone prevents itself from transmitting on frequencies which are not licensed for cellular use in certain locations.
Thirty five thousand feet is only ~6.6 miles assuming you are more or less on top of the transmitting cell tower, which is a perfectly feasible distance for a cell phone signal to travel, especially given that there will not be any obstructions between the phone and the tower other than the airplane itself. There are other technical reasons why your phone might not work well
at altitude, and why using your phone at altitude is detrimental to the operation of the cellular network, but the problem is not that you are too far away to receive a signal.
If you don't want it known, don't say it on a phone.