Gosh, when I was a teenager, I would spend hours on the phone with my boyfriend. It is best advised to stay away from subjects that can lead to an argument. Talk about your hopes and dreams, share with him what you see as a probable future. Talk about the things that interest him, ask him to tell you about his day, and then, really listen. Make sure the conversation is two way. Not just you telling him and doing all the talking. Make plans for the weekend, or to go to a movie. Talk about what kind of movie you would both like to watch. There are an incredible amount of topics you can discover, but let it flow naturally. A forced conversation won't go to far, and if there is a long pause, people often used to say, an angel just flew over. If he asks you what that means, you tell him that in a moment of silence, it used to be believed that an angel flew over. This in itself may become a topic of conversation
