Unfortunately, lots of laws are made to protect people's privacy, and usually the only ones who need the protection in these cases are the criminals. You can thank the ACLU for that.
Anyhow, if done fast, find my friends/iPhone is an excellent way to keep track of the phone. A guy came into the Pct. I was working in one day a few months ago and said someone stole his iPhone. So he showed me his girlfriend's iPhone (I did not have one at the time, so this really amazed me) and it showed me the exact location to the point we were watching it move down the street on the screen. So we loaded him into a car and took a ride to where it was on the phone. The victim pointed it out the guy who stole his phone, and it was recovered. Bad guy got new bracelets. Good guy got his phone back.
But again, this only works when done immediately.
Phone wasn't impounded?
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But they won't.
While technologically possible, they never ever do this unless there is an emergency.
Or a court order.
ATT is not in the phone tracking business and has no staff for this activity.