Melanie's Hot Line (1975)

An obscene telephone call leads a young couple into a world of bizarre sex sparked by the mysterious voices on the other end of the line. A cyclone of indecent lust and perversion follows as we watch one deviant call the next, each with an increasingly lurid exhibition in which pain, pleasure and lasciviousness tell the mind warping story of the San Francisco underground sex culture. When they all meet up in the end, all rules are broken.