It's interesting to see the look of shock on a sales clerk's face when they ask "Can I have your phone number please?" as they begin to ring up my purchase, and I say "No." It's particularly fun when they clerk is a nice-looking woman and instead of saying "No." I'll ask, leeringly, "Can I have YOURS?". Point: A good first step is to stop giving out seemingly inoccuous information whenever asked. JUST SAY NO.