I think it depends on:
a) what you are fighting about. Some topics should not be brought up in front of the kids, including if you are having a disagreement about your parenting methods.
Couldn't agree more. Too many people think their children are too little to understand. I think whether you are on the phone or in earshot or in front of them you need to be conscious about what your children can hear. I have memories of conversations I was too little to understand them, but as I got older I remembered and it wasn't pleasant. My philosophy is if your child understands basic commands then you apply this then. Not only does it get you into good practice but you aren't going to know when exactly they go from not understanding to understanding.