They listen to whom they *want* to listen to - because it would take *significant* resources, manpower and equipment to 'listen to everybody' -
- as it *would* take *real* connections, *real* access to infrastructure, etc, to monitor *every* 'phone call' in progress and every "phone call" is *not* connected from point A to point B via satellite during a call -
- WIRE or FIBER OPTICS are by far the cheaper means used to inter-tie local local phone exchanges via the ;ong-distance networkd ... even overseas calls (ever remember hearing the term trans-atlantic cable?) are via cable ...
The rest, the hype, is common mis-information ...