Or to make reservations to use the telephone. The availability requirement raises cost considerations. Equipment which costs less is more likely to be available. But cost is not the sole, or even the primary determinant. If some technology meets the other criteria as described below, it will be made widely available, despite the cost.
Good technology is always on .
Or if not always on, can be turned on with a single one-stroke command, or better yet, start automatically when the need arises. One thing which makes the telephone useful is that we do not need to boot up the operating system before we make a call. Electrical lights are a significant improvement over systems which required individual ignition with a match or candle. Streetlights are practical because they turn on when it gets dark outside. Much of today's educational technology requires long and sometimes cumbersome initialization procedures.