Can anyone tell me how to program USB devices with Objective-C as an iPhone application?
I want to access USB device contents through iPhone
You can't. While it is possible to build USB based accessories for iPhone if you join the Made for iPhone program using the ExternalAccessory framework, you cannot access arbitrary USB devices. The SDK gives you access to devices that use a custom interface on top of USB, the exact details of which you get after signing up for the program and singing some more NDAs.
来源：https://stackoverflow.com/questions/1678681/usb-programming-with-objective-c