Deathline (1996)

Main character is Conny, a city-girl, working daytime in a hospital as telephone-receptionist, but in the evening at a telephone-sex agency. Realizing, that her life is not very exciting and neither is her relationship with a doctor at the clinic, she is easily and naively fascinated by fantasies and strange and colorful things. Always wearing a trendy, short-clothed city style, she gets dangerously involved in a more and more intimate telephone-sex relationship with an anonymous customer called Der Kalte Finger. Quitting the agency she 'works' from home with her new special customer, realizing too late that he lives his fantasies in the reality and could be the murderer of several girls recently found dead.