Chapter 9 of my book on technology transfer or sales or what have you will be devoted to smiles. I realize that the research here is deep, however my direct experience is related to making the follow up call. In my business as an intermediary, I often find myself reminding one party or the other to complete a previously agreed upon task. Most (read: all) of the time the task is not completed. One of my secrets is to smile as I am dialing and right before I leave the voicemail. In my purely qualitative study, I have found that my messages are upbeat and nearly all of my targets thank me for what I affectionately describe as a pleasantly persistent phone call.
I just ran across a fascinating description of the impact of smiling on sports performance, success and even life expectancy. I know that smiling make me feel better and that is good enough for me.