Earlier quoted context omitted.
You can't. You have to sign up for the dev program to get the app on your device. You can program to the simulator, but that doesn't help you with the unique features of the phone (camera, accelerometer, etc).
Or you can jailbreak, which lets you run unsigned apps including ones that you build in Xcode. But yeah, developing exclusively for the iPhone is just handing Apple a kill switch to your company.
Imagine if you had to jailbreak your Windows machine to use applications that Microsoft hadn't approved...