Only once, in the days before cell phones became common. I called my office voicemail from the lounge just as my plane started boarding and discovered that the organization arranging/hosting my trip had made a mistake and failed to either confirm my hotel reservation or inform me earlier that there was a problem. I talked to them during the flight to have them find me a room in a city that was essentially sold out due to a major special event. I forget what the airphone charges were, but not sleeping in the street that night was priceless.