my wife and I both have iphones, and we both bought all 4 maps - at 3.96 for all 4 (99 cents each), it's the best Disney item you can ever buy.
The maps are always with you, and in a convenient size, and something easy to carry.
If you are in MK, and want to look at something at AK or Epcot, then you can do it very easily - much easier than carrying around all 4 fold out maps.