It would be nice to know if a teen was texting when they smacked your bumper and caused over $2,000 worth of damage though. Happened to me a few years ago and yes she was texting.
“Nice to know” doesn’t justify illegal search and seizure. Besides, if they need to know if the cell phone was active, they can subpoena the records from the cell phone company and determine perfectly accurately. No need to allow warrant less searches by cops.
As many astute Americans noted after the school massacre in Newtown, CT ... your misfortune doesn't allow you to trample on anyone else's Constitutional rights.