I used an ipod Touch for a couple of years before I got an iPhone, and the software works great in the Touch.
Two things now with an iPhone that you can't do with the touch -
1. Instant weather conditions from the nearest weather site are downloaded into your favorite program. No, you don't have an included weather meter
but often it's far closer than using standard parameters.
2. GPS ability with the phone allows me to leave my separate (and larger) GPS at home.
There are more advantages to having the phone, but those two come to mind immediately when thinking of hunting and shooting.