Speakerphone Rules

I called my friend at work a while ago and we chatted about our plans for the night, a few of our mutual friends, and I made some derisive comments about his co-workers without a second thought. Towards the end of our five-minute conversation I asked, "What's that tinny noise, are you driving?" "No man," he said, "you're on speakerphone; I'm at work." I know he works in an open space with several other people, I only hope they weren't there. Or at least the ones I was talking about. The ethics of speakerphone are that you: 1. Have to tell the person right away that they're on speaker phone, and 2. You only ever use it when you're alone.