Mobiles in Mass

Forgive if slightly off topic but read a story a few years ago about an accident that took place on a motorway somewhere in the U.K. A few people had seen a guy on his mobile so flagged him down and asked him if they could call the emergency services. He had to apologise as it was only a plastic phone.
 
I'm very surprised actually that the Bishops haven't instructed priests to take 10 seconds at the start of each mass to request all those present to turn off their phones.
Have priests that little power that they would have to wait until a Bishop instructed them to ask people to turn off their phones. I have been at a number off Masses that the priest announced before Mass started that all phone should be turn off.