When Jack Dorsey sent out the first Tweet ever in 2006--"Just setting up my twttr"--few would have guessed that the service would eventually play a key role in everything from elections to citizen uprisings in the Middle East. (Even the founders didn't know what to make of Twitter.) Become a real company with a working business model? That was perhaps even harder to picture. But become a business Twitter did--in fact, a soon-to-be public business that reported $317 million in revenue in 2012. Read on to revisit Twitter's major milestones over the last nine years.