At my old job (Insurance Adjuster) we were always told, "Make sure you smile when you're on the phone and are friendly to each and every client. You may talk to dozens of them a day, but you might be the only voice they hear. " Because of that, I still smile at everyone and make sure I'm friendly to everyone
On a side note, I had a lady tell me at work (waitressing) yesterday while I was running around like crazy "Honey, slow down, you don't get paid enough to work" I just smiled and said that I didn't like to make people wait. She responded "No one here is starving to the point they can't wait an extra 30 seconds" It felt so good to be recognized as working hard