The expression functions as an interjection, typically used to express surprise or disbelief upon receiving unexpected news or information. It conveys a sense of shock or the need to pause and process something surprising. An example usage would be, upon hearing an unbelievable rumor, one might exclaim the phrase to indicate their astonishment and request a moment to absorb the information.
Its importance lies in its ability to succinctly communicate a complex emotional reaction. It offers a culturally understood way to express incredulity or amazement. The phrase likely originates from a desire to physically halt a conversation or action to fully consider a surprising revelation, drawing upon the imagery of physically holding a telephone receiver to interrupt a call.