I remember that the detectives working on the Soham case in 2002 sent a voicemail to one of the missing girl's phones and then appealed on TV for their abductor to listen to the message. At the time this seemed like quite a strange thing for the detectives to do (people were a lot less savvy about phone evidence back then). It got a lot of coverage in the press.
In retrospect I wonder if it was a stingray-type gambit, whereby if the abductor turned the phone on they would be able to trace exactly where they were. I don't think it got mentioned in court so perhaps it was unofficial/inadmissable
https://www.theguardian.com/uk/2002/aug/15/childprotection.c...