1) A clear dial tone (even if it's a fake dial tone) to let me know that the numbers I'm typing in shall be part of a call and not anything weird.
2) No fiddly little buttons on the side of the phone that I have to try not to hit while talking on it.
3) The mouthpiece should be set up such that it can pick up background and/or distant and/or quiet sounds.
4) One should be able to dial a number or fiddle with the keypad while the phone is still to one's ear, without trying to do some weird "look at your own ear" thing.
What does this seem to add up to?
Seems I don't really want a cell phone. All the "handy features" of cell phones seem to be things that I consider disadvantages.