Simple.

Receiving a phone call is simple. But when your phone rings, pulling you out of your papers and study guides and busy work, you realize that the person on the other line is actively concentrating his or her attention on you and has been for at least as long as it takes to decide to call you. If it's an important call, they may have even wondered what to say or imagined how you might react.

And sometimes that's really nice to think about.