When you guys were first dreaming up Twitter, what did you want it to be? And how different is the reality than what you had envisioned? It grew much bigger much faster. But it's fairly close to what we had envisioned. We envisioned being able to, at a glance, see what friends and colleagues were doing. We wanted it to be a freeing way of communicating.

We were actually inspired by looking at an AOL IM buddy list. If you just look at the status messages, they're like "Out getting coffee," or "Out sick," or "Too busy to talk." We were thinking about that simple information, and our co-founder Jack Dorsey had a history in dispatch for ambulances and such. He had an interest in knowing at a glance where people were and what their status was. We knew there was a benefit to putting this information together.

We also knew that having access to these seemingly trivial bits of information was not trivial. Each bit of information is kind of insignificant, but having access to it all is a powerful tool.

Why did you choose 140 characters?Why not 135 or 17? SMS has a limit of 160 characters, and we wanted to save 20 characters so you could see the name of the person who wrote the update. We wanted you to be able to read the update on any device and not have the piece cut off partway.

A lot of people say Twitter has changed the Internet. What's your take on that?I think it does have the potential to really expand it. What inspires me is to expand the power of a real-time network to the weakest of signals around the world. We've had these great user cases, like this guy who got himself out of jail in Egypt. Farmers checking in and saying, "This is what price I'm getting for my grains. Is this a good price?" I think we can extend this a lot more and build it into mobile in a unique and compelling way. SMS is on every phone and super simple.

How do you plan on making it more mobile? Right now, anyone in the world can update their Twitter through SMS, but we only send out updates on SMS in the United States. We receive them from everywhere, but we only send them in the U.S., and that's because of cost. We need to go to each country and negotiate a deal that makes sense for us. That's one way we're going to expand the mobile aspect of Twitter.