i think technically it needs to be a host capable usb device, if you can attach usb perpherals which tend to be slave devices like keyboards, mice, usb flash drives etc etc to the iphone then it would probably be possible to make software the iphone to program the speed controllers like castlelink.

I know my Nokia n800 internet tablet can turn its usb port into master mode so you can use external usb slave devices like usb wifi adapters etc.