[kinghajj]

FBI: "Hey, cellular provider, give us the secret key and ID for X." Provider: "Sure, thing, just one moment." ... "Here you go."

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Or, if your provider has a bit of a spine:

FBI: "Hey, cellular provider, give us the secret key and ID for X." Provider: "Got a warrant?" FBI: "No problem, give a half hour to call our go-to judge." / "No, but here's a NSL."

[doctorshady]

That's assuming that is even necessary. Harris made an upgrade to their Stingray equipment called Hailstorm that intercepts 3G and 4G standards.