Why unenforceable? All they have to do is have a database of phone identifying numbers. Then as soon as a phone dares to tap another network, the drones can zero in...
Now we know why the FEDS bought a BILLION BULLETS.
It’s unenforceable because there is no such database, and law enforcement doesn’t have the means to obtain one legally. When I purchase a phone, I don’t have to register it with the government and there is no law forcing me to do so.
Besides, anytime you try to enforce a rule like this having to do with computing, you are engaging in an exercise in futility. Computer techies (we used to all be called hackers, before that got negative connotations) love to find ways to make things do what they weren’t supposed to do, or to break the “rules” and get away with it. It’s in our nature, and so we will very quickly apply our collective brain power to defeat any plan like this.