USB_ModeSwitch is a mode switching tool for controlling "flip flop"
(multiple device) USB gear.
Several new USB devices (especially high-speed wireless WAN stuff,
they're expensive anyway) have their Windows drivers onboard; when
plugged in for the first time they act like a flash storage and start
installing the driver from there. After that (and on every consecutive
plugging) this driver switches the mode internally, the storage device
vanishes (in most cases), and a new device (like an USB modem) shows
up. The WWAN gear maker Option calls that feature "ZeroCD (TM)".