Speaking as a fan of Lucille Fletcher's "Sorry, Wrong Number," the famous radio play, this version, adapted by Fletcher herself is surprisingly good -- especially given that the story has been fleshed out threefold.
For the uninitiated, Mrs. Henry Stevenson is an invalid who is confined to her bed. Her husband, who was supposed to be home hours ago, has yet to show. In trying to get him on the telephone (this was the age when operators still did all the work for you), she is crossed into another conversation between two men who are planning to kill a woman at 11:15 that night. Having a heart condition, this upsets Mrs. Stevenson ("Leona" in the film; radio did not give her a first name) and she tries several things to notify authorities.
Due to her highstrung manner and short temper, she doesn't get much anywhere and the night passes on as she spends all her time on the telephone. All the time, 11:15 is getting closer...
Barbara Stanwyck was nominated for an Oscar for her performance in Sorry, Wrong Number (the radio play also made a star of Agnes Moorehead), and it certainly is a tour de force with her in practically every scene. Lucille Fletcher's expansion of her storyline is superb, with more and more details given as pieces of the puzzle unfold with each new telephone conversation, told through flashbacks (and flashbacks within flashbacks). In fact, my only problem with the script is that it makes the husband sympathetic (probably because he is played by Burt Lancaster), whereas we had no inkling of the motives of the husband in the radio version (other than that his wife is a shrill shrew, of course).
Comic relief is also added (particularly in the police station) to little effect and the whole enterprise is simply missing something. Although I can't think of one specific thing that is wrong, the whole film just doesn't gel somehow. It's a good watch, I assure you, but I can only conjecture as to how it has attained its "classic" status. I think it must lie in the fact that it stars Barbara Stanwyck and Burt Lancaster and that Stanwyck gives a complex bravura performance.
But despite all this, I can't imagine ever wanting to see Sorry, Wrong Number again. The similarities to the radio show are there, and it's faithful, but the rest -- even with all the intrigue about gangsters and stolen money -- just seems like so much filler. I'll stick with radio.