Sam, assuming that you are referring to cellular data feeding wifi, It depends which country you are in. My observation is that across the flatlands of N Europe 1500' seems to be the limit. In the S of France, the Western US and throughout NZ you can get data at 10,000' within about 30 mi of habitation. Doubtless mountainous terrain is a factor.
With regard to airborne devices 'jamming up' the cell towers, they must daily be subjected to thousands of airline passengers who leave their devices on during flight, although they may only spend a few minutes in the critical height range. Our presence must be negligible compared with that.