Twitter is the first form of communication that changes depending on who is using it. Like the telephone, the fax, email, Twitter enables all types of communications: friendly banter, customer support requests, news syndication and public service announcements to name a few.
But Twitter imposes a three new wrinkles that set it apart as a new form of communication. First, the recipients of a tweet are knowable but never really known. One could sift through a list of Twitter followers but never understand who they are, if they pay attention to tweets, why they follow an account, or what agenda they have. Followers might include close friends, business acquaintances, customers, strangers and Justin Bieber - or any combination.
Second, a user's experience with Twitter changes based upon their following. Sending a tweet falls somewhere along the continuum of yelling into the woods when no one else is around, practicing Shakespeare in a crowded public park or stumping on stage in front of 100,000 people in the audience with a microphone in hand. A Twitter user's follower count molds his Twitter experience.
Third, Twitter is the only communication form that doesn't require systematic processing of messages. Most of us respond to email, SMS, voice mail and phone calls with dogmatic diligence. In the Twitter stream, users are panning for gold, balancing signal and noise in a much more equal quantities than voicemail. Missing a few thousand tweets doesn't really matter.
These three properties of Twitter enable users to bend and shape their experiences as they wish. It's this plasticity that makes Twitter such a novel communication platform. We each have to learn how to use it, as we use it.