I am currently reading The Design of Everyday Things. It is a great book, although it has often made me angry at the designers of doors and stove tops :)
In the section about memory Norman discusses the importance of reminders. There is some clever stuff in this chapter. He makes this statement.
Would you like a pocket-size device that reminded you of each appointment and daily event? I would. I am waiting for the day when portable computers become small enough that I can keep one with me at all times. I will definitely put all my reminding burdens upon it. It has to be small. It has to be convenient to use. And it has to be relatively powerful, at least by today's standards. It has to have a full, standard typewriter keyboard and a reasonably large display. It needs good graphics, because that makes a tremendous difference in usability, and a lot of memory - a huge amount, actually. And it should be easy to hook up to the telephone; I need to connect it to my home and laboratory computers. Of course, it should be relatively inexpensive.
I read that and thought wow this guy new the iPhone back in 1988 (first edition of the book). But, instead of having to hook it up to the phone, it is the phone.