It's a Richard Rogers (music) and Lorenz Hart (lyrics) song from 1932 called "Lover". Jeanette McDonald sang it in the movie "Love Me Tonight", and it has been recorded by different artists (Guy Lombardo, Frank Sinatra, Harry James, Ella Fitzgerald to name a few) and used in many other movies (including Alfred Hitchcock's "Rear Window"). It was later recorded in an up-tempo version by Peggy Lee, which is the version most people are familiar with.

No, the film was adapted from a 1943 radio play written by American screenwriter Lucille Fletcher, who also wrote the screenplay for the movie, expanding the 22-minute radio play into an 89-minute movie by adding 67 minutes of backstory. A TV version of the movie, Sorry, Wrong Number (1989), was released in 1989.

At 9:24 PM, spoiled and wealthy 'cough drop queen' Leona Stevenson (Barbara Stanwyck), an invalid confined to her bed, attempts to call her husband Henry (Burt Lancaster) at his office when he doesn't return home at the time he promised. Somehow, the telephone wires get crossed, and she ends up hearing what she thinks is a plot to murder her at 11:15 PM. She begins making a series of telephone calls to the operator, to the police, to her husband's secretary, even to her husband's ex-girlfriend. Eventually, the story unfolds that her husband is being blackmailed and may have arranged her murder so as to collect on her life insurance.

Leona thinks that she's having heart attacks brought on by stressful situations, a condition from which she has suffered since childhood. However, Dr Anderson (Wendell Corey) diagnoses her as a 'cardiac neurotic' and believes that her heart attacks are psychosomatic. In today's terminology, cardiac neurosis might be referred to as 'panic attacks', which actually can show symptoms similar to a heart attack, e.g., heart palpitations, sweating, chest pain, weakness, shortness of breath, and tachycardia (rapid heart beat).

The clock strikes 11 PM. Becoming more and more scared, Leona phones Bellevue Hospital to hire a nurse, but they don't provide that service. Meanwhile, the shadow of a man can be seen entering the house through an open window. Suddenly Leona hears a click on the phone, as though someone has picked up the extension. Terrified, she hangs up and begins screaming at the person in the house, hoping it is Henry. The phone rings; it is Henry calling from New Haven (Connecticut) on his way to Boston (Massachusetts). Leona tells him everything Waldo Evans (Harold Vermilyea) told her and apologizes for being so mean to him. 'I only did it because I love you,' she cries, 'and I thought you didn't love me!' She assures him that, if he had told her about needing the money, she would have gladly given it to him. Henry looks at the clock outside the phone booth. 11:10 PM. Henry pleads with Leona to get out of bed, go to the window, and scream 'or you've only got three minutes to live', but she is too frightened to move. Henry confesses to everything, but he is cut off by Leona's cries as she sees the shadow of a man coming up the stairs. The man enters her bedroom, and Leona screams just as a train goes by. Her hand can then be seen flopping on the night table. In the final scene, the killer picks up the telephone receiver and says, 'Sorry, wrong number.'