Cellphone Surprise

Jeff is a 53-year-old single man, who has not yet mastered the modern marvels of the cell phone. He started a new job driving a large truck hauling dirt. The first day his boss, Mary asked him to carry a cell phone with him in the truck in case she needed to call him.
"I don't have a cell phone."
"You can take mine."
Jeff thanked Mary, and dutifully carried the cell phone in the cab of the truck every day as he picked up and delivered his haul. Each day at about the same time, music would suddenly start playing in the truck. He checked the radio to see if it was on, and then remembered that it was not working. The windows were rolled up. The music would play for just a few minutes and then stop. For three weeks this went on.
One day his boss asked, "Jeff, why don't you ever answer the phone when I call you?"
"It never rang. I would have answered it, if I had heard it ring. You know what though? Every day at about the same time, music starts playing in the truck. I can't figure out where it's coming from. The radio is off, and the windows are up, and then out of no where music starts to play."
"What kind of music?" Mary asked
"Well, that's the funny thing. It's always the same tune. I keep hearing, "Hit me baby one more time" by Britney Spears. It plays for about a minute and then stops."
Mary looked him square in the eye and deadpanned, "Next time you hear the music, pick up the cell phone."
Jeff hasn't missed a call since.