The problem with the cell phone is that perhaps his mother wouldn’t be home. He knew his phone number but his mother was out looking for him. By staying in a public place like a store, a child is most likely safe because usually the child wouoldn’t be alone with an adult in a store. It is very public. Standing on a corner dialing a phone doesn’t sound to me any safer. Besides, can you hear the g’shrai when cell phones are given out to 9 year olds? My sons’ hs didn’t let them have cell phones for any reason.
Unfortunatally, you can’t prevent every tragedy. You can teach your children NEVER to get into a car with ANYONE they don’t know no matter how frum the person looks.