Talking to oneself in public

I have noticed the frequency to which people have seemingly personal conversations in public. These are taking place more and more without seeing the other person face to face. Cell phones abound everywhere. The thing that still catches me off guard are the handsfree sets, so you can't tell if the person is rambling to themselves, you, or just whoever will listen. Now I understand people have had private conversations in public for hundreds of years. But there are some difficulties in keeping the nature of information private which cell phones have introduced. For instance reception, if the person can't hear you, then one begins to shout without realizing that they are not the only one in the room. Mouthing the words just doesn't work over the phone either. Same goes for head nods and diverting one's eyes towards the foolish stranger. It is a lot harder to talk about someone without them knowing, when you are within earshot if one is on the phone. Perhaps code, or lingo will evolve to fill the private gossip gap, but for now people with cell phones need to be on their guard.