Odeo released Twttr today, a new tool which helps you stay in touch with your friends through SMS. Currently open only in the U.S. and Canada, the idea is fairly simple. You can send updates on your self (your location, what you're doing, etc.) to a centralized phone number (40404 in the U.S. and 415-283-8611 in Canda) which those on your friends list will then recieve, and they can choose to do likewise, in a way never losing touch.
I think the idea is adequately competant in this general teen/young adult market of minutely txt'ers, although I'm a bit unsure of how revolutionary this really is. Most phones these days have the ability to make 'lists' of friends to which you can send messages to, and Twttr only seems a more focused, organised and centralised version of this.
What interests me most about Twttr is their business model. Currently, it's completely free as it is although they might end up adding premium services which they charge for later on. This is the general route for most applications in Web 2.0, but does it really work? Dodgeball, Twttr's closest competitor which Google acquired last year have worked with a similar plan and even though have the users, it's still unclear how they think of making money.