In December, with major flight disruptions at AMS, a direct message to Delta on Twitter was answered promptly and got me rebooked on a new flight to the US for the next day before my turn in line came up to be helped at the KLM lounge. Last Saturday, it took over 4 hours for a direct message to be answered, but they were able to take care of my request quickly once the conversation got started. The PM phone line was useless last Friday--one-hour-plus wait times plus a failed callback, but at least I was able to find a lower overall fare than the one I was trying to book by phone (child fare for the itinerary DL's website gave me) while I was waiting.