It's also a surveillance device in its design. The mechanism of it is to connect to one or more third-party-owned towers to bidirectionally transpond data. By the nature of the machine, calculating roughly where the machine is every time it transponds is very straightforward.
"I want to send and receive messages from you but you're not allowed to know anything about me" is, at first pass, a tall order. We can sort of get that from the postal system and very little else in terms of communications technologies (and even then, if you screw with the network the postal service in the US is empowered federally to hunt you down).
"I want to send and receive messages from you but you're not allowed to know anything about me" is, at first pass, a tall order. We can sort of get that from the postal system and very little else in terms of communications technologies (and even then, if you screw with the network the postal service in the US is empowered federally to hunt you down).