Lot of people involves in Iphone games with 3D engines supporting them more and more. Apples Istore is a the key of the success also !
I know that not going in details with Gimp 2 or Zbrush can be frustrating a lot, specially when you can achieve great details and things with great 2D and 3D software

If i had to make very low poly characters for Iphone i think
i would go from some software like 3D Coat and do a Retopo to make it. It would save lot of time caus i would have the base texture OK with a baked normal map.
But for a skilled texture artist, the traditionnal method of modeling and texturing would do as good and better sometimes !