Via CNN [emphasis added]:
James Karl Buck was released from a Mahalla jail after sending a one-word blog post from his cell phone through the Twitter Web site. The message -- "Arrested" -- alerted all of his friends on the site of his detention. Twitter, a social-networking blog site, allows users to send status updates, or "tweets," from cell phones, instant messaging services and Facebook in less than 140 characters. That message helped free Buck, whose college hired a lawyer for him, but it didn't help free Mohammed Maree.
And no, I wasn't familiar with Twitter, either, before I read this article.