All you need to do is speak in your head. Dont just think, though, you need to make the words in your mind without worrying about moving your lips. The computer will then capture the chatter and send it over the internet to your friends PC, which will speak your thoughts. This might all sound like science fiction, but TI has recently demonstrated a system that picks up the electric nerve signals travelling between the brain and the vocal chords. using a pre-programmed vocabulary it then anylises the nerve data and creates digital speech. All the speaker needs to do is wear a neck band sensor.
The current system only has a vocabulary of only 150 words and the resulting voice is rather robotic, but TI is working on it.