A buddy of mine who had the same aversion you seem to have to using a dayplanner or scheduler got a PocketPC/cell, using the same logic you do. (You have the cell all the time, and you'll use the PDA because it's also your cell) It ended up being a complete waste because if you aren't a scheduler kind of person, a PDA/cell isn't going to make any difference, regardless of it being on your cell or not.

If you insist on getting one of the four, I vote for the Samsung i700. It's laid out so that to use it as a cell you'll have to use it as a PDA anyway, which will force you to at least try to use it's features (and your money won't be a waste). And right now, Samsung and Motorola are the two brands that are really putting out quality stuff in terms of cell phones.

However, I still stick by my opinion that if other scheduler techniques haven't worked in the past, a PDA won't change anything. Use the coupon and go nuts on a really nice phone like the V710