I often think about why this about a payphone. In today's world, no one uses them, and I think that is the point of the song. Adam is singing about the past when he was at a payphone trying to get this girl to stay with him, but it didn't work. Now, he is successful and has changed his number (probably to his cell phone) so that she can't even call him. Yet, in his memory, there is still a part of him at that payphone remembering how much was wasted on a relationship that went wrong.