Perhaps Twitter is like interesting people from around the world texting and sometimes I text back? But it is more than that. I get most of my news through Twitter and it is like instant messaging with various friends and colleagues and heroes and comedians and ... I used to describe Twitter as being like just the status postings from Facebook. But Facebook has changed so much since then that I'm not sure that description still applies. And the network of people you interact with on Facebook and Twitter are quite different (certainly, the way I use those services).
But, really, Twitter isn't like texting or RSS feeds or instant messaging or Facebooking. Or, actually, it is kind of like all of those things and more and less, all at once.