I am a pilot and an aircraft owner. My aircraft is certified and fully equipped for IFR using traditional navaids (I have two nav radios, one with a VOR/LOC indicator and the other with a VOR/LOC/GS indicator). I also have a WAAS GPS receiver which I use for navigation.
GPS operates in the L1 band with a carrier frequency of 1575.42 MHz and a bandwidth of 13.345 MHz.
The telcos are operating "5G" channels with carriers between 1475 - 1518 MHz and bandwidths of up to 20 MHz.
I can tell you that very recently, when I pass over certain urban areas near newly erected 5G towers, the GPS reception goes bonkers. It's really disconcerting when you are flying the plane for your annunciator to start yelling "terrain pull up" at you when you are at 3000' AGL. The frequency allocations are just too close together. You could put really narrow bandpass filters on the GPS receivers in aircraft, but this will be a very, very expensive process and will be very time consuming. All the avionics shops in the southeast are backed up for months and months. Filters installed in aircraft require TSO approval, and a change in equipment requires that the IFR certification on the aircraft be redone.
Three of these towers just went up around my hometown in the mountains of North Carolina... Someday soon, someone's annunciation system won't go off and a pilot flying in unfamiliar territory or in a high workload situation is going to fly an aircraft into the side of a mountain who would have otherwise lived.
I see a lot of propaganda out there from the telcos saying that planes are not falling out of the sky in other countries... but airspace conditions and radio spectrum congestion are a lot different in other countries (as are the frequencies themselves). Remember, just about everyone in this country will eventually have a transmitter operating in this spectrum in their pockets.
How many people need to die before the government realizes how badly they screwed up and does something to solve the problem? Either shift the frequency allocation, or subsidize the retrofitting of the aircraft navigation systems. Regardless, this is going to take a lot of time.