Being mindful while talking now there's a challenge. Not that it's the only thing it's hard to be mindful of (especially when we're trained not to be, by our whole culture).
We do have some experience of it. For example when you teach, you accomplish more if you notice how you are doing it, and how it's received. Or if you study any program that requires you to learn new ways of relating to other people, you need to speak mindfully to succeed.
But it's so easy to blurt out the soundtrack of our current mindtrip. It's one of the reasons I like writing; I have a slightly greater chance of thinking before I put the words out in the world.