R.L. Stine 
Wrong Number 

It begins as an innocent prank: Deena Martinson and her best friend, Jade Smith, make sexy phone calls to the boys from school. But Deenas half-brother, Chuck, catches them in the act and threatens to tell their parentsunless the girls let him in on the fun. Chuck begins making random calls, threatening anyone who answers. Its dangerous and exciting. The teens are even enjoying the publicity and the uproar theyve caused. Until Chuck calls a number on Fear Street.