Computers are so powerful, so transformative, and still so new that they stand out. But the telephone has become so invisibly, powerfully utilitarian that we barely think about it anymore, and that's an attribute that is worth understanding when building good Web apps. It's useful to think about each of these technologies in its relationship to time and our subjective experience of it. When we watch TV, we have to synchronize our time with the time of all of the available channels so that we can tap into the stream of programming. When we find something we want to watch, we allow ourselves to be immersed in the flowing current that the program provides.
Computers are nothing like TVs.
All Web users have probably gone through that initial period of discovery where they surf from page to page and lose all sense of time as they become immersed in the experience. Flow happens when our actions and the reactions of the application hit the right balance of effort and reward, and time just disappears. Telephones are radically different. When we answer a ringing phone, we immediately collapse the distance between ourselves and the person we're talking to. We're extending ourselves to another person, yet our sense of time is unaffected.