I seem to remember that Twitter was conceived as a simple-to-use replacement for SMS, originally. SMS still has about 3 billion users, so the market for short text messaging is clearly there. In terms of Twitter, I can see its value for, say - people at a conference, where it would be simple to keep track of colleagues and pals through the service, but I also suspect that Twitter will eventually - through add-on features and advertising - possibly lose its appeal and even functionality. On the other hand , processor speeds continue to increase, so maybe not. At the moment, it's probably the nearest we'll get to telepathy for while.