On twitter, if you begin a message with someone's name, it will appear in the target person's news stream, and no one else's. (The message is still public, but the untargeted person must visit the senders page to see the complete list of messages)
@janPolo ni li musi mute! (janPolo can see the message with ease, but everyone else will have to visit twitter.com/janMato to see that message.
To turn these messages of general interest back into broadcast messages, one must put something in front of the name.
o @janPolo ni li mute mute! (Now this will show in the message streams of all my followers, although janPolo will know he was the person in specific being addressed)
Now what is wrong with this? Vocatives are for marking who I'm talking to. But on Twitter, including the vocative has the effect of meaning, "Hey everyone, listen to what I have to say to @so_and_so!"
Since tp is an internet language, I suppose phrases and mechanisms will evolve soon for the other similar situation, the to: cc: and bcc: sections of an email message.
* o jan Mo! soso jan Ko en jan Somo! [bososo jan Do] ni li musi kin!