Buying an Apple iTouch / iPhoneIt is absolutely critical, if you are developing applications FOR an iTouch / iPhone, that you OWN an iTouch or iPhone. You need to have worked with many applications on this platform to know what people are going to expect. You need to have your app work as "normally" as possible.
I was in good shape in this case - I had bought an iTouch a while bach to do game reviews on. I write gaming reviews for BellaOnline and have most of the handheld gaming systems as well as all of the main console systems. The iTouch is a unit I bought as a "matter of course" when it came out. I've downloaded many apps for it along the way.
Where iPods (the music players) normally have a big wheel and no touch screen, the iTouch and iPhone are both designed with their entire viewing face being a touchable screen. Not only that, but they have sensors in them to know if you have rotated the screen vertically or horizontally and will shift the display to match.
The main difference between the iTouch and the iPhone is that the iPhone has phone service. That can be a LOT of extra money. So it is fine to just get an iTouch and not pay for that monthly phone service charge. That being said, with the iPhone you can do cool things with your app like have it call the restaurants you look up, know what restaurants are nearby based on your location, and so on. So if your app is in any way "location based" it is worth it to splurge to get yourself an iPhone and be able to test that properly.
iTouch from Amazon.com
Creating an iPhone App
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