Listen (1996)

Sarah, a San Francisco accountant, moves into a new apartment building to be near her new boyfriend Jake, a writer with a case of writers block. When Jake has trouble with intimacy with Sarah, she escapes by eavesdropping on others people's phone lines and soon suspects that a man's voice on a phone sex line is a serial killer that is killing prostitutes all over the city on a nightly basis. Sarah then enlists the help of her girlfriend/ex-lover, Krista, to find the killer's identity before the killer finds them.