you should technically be able to, but looks like they dropped this feature if the rev b version, which is what I bought.
and I bought this router cause it was the only one I'd seen that had this feature, that you could plug in a usb cell device and use it as a backup if the wan link were to drop.
ho hum, if you ever get it working somehow, post back, but I called dlink and was basically given the verbal finger, it's no longer an option and won't be added back...ho hum.