It gets really funny/complicated with some devices. For instance, I have a Sony Ericsson PC-300 3G data card. It's built on the NEC USB chip and uses the internal hub to connect the SIM reader and the 3G modem (with some other device, as well.)
Alot of express cards are just usb devices. I bought an express card serial card thinking it would be better than a usb one, but it's identical.
