Students. I'm not sure if devs still get hardware discounts or not but to get them I'm pretty sure you had to be one of the devs that pays $3500 (or whatever the cost was) for developer membership. (I could be wrong on the price but I'm almost positive I remember seeing that.)
Once you get your student discount though, also go to developer.apple.com and register to be an iPhone dev, however to put your apps on the device you need to pay $99 for a year which is dirt cheap considering what Apple does for you. (Anyone who thinks otherwise must not appreciate the free app hosting).
If you are new to development, hold off on paying that until you get to learning Cocoa (You will need to learn Objective-C first). Once you get to Cocoa though I'd recommend using both the simulator and paying the $99 to put your apps on the device.