Several new USB devices have their proprietary Windows drivers onboard, most of them WWAN and WLAN dongles. When plugged in for the first time, they act like a flash storage and start installing the Windows driver from there. If the driver is already installed, it makes the storage device disappear and a new device, mainly composite with modem ports, shows up.
On Linux, in most cases the drivers are available as kernel modules, such as "usbserial" or "option". However, the device initially binds to "usb-storage" by default. usb_modeswitch can then send a provided bulk message (most likely a mass storage command) to the device; this message has to be determined by analyzing the actions of the Windows driver.
In some cases, USB control commands are used for switching. These cases are handled by custom functions, and no bulk message needs to be provided.
Usually, the program is distributed with a set of configurations for many known devices, which allows a fully automatic handling of a device upon insertion, made possible by combining usb_modeswitch with the wrapper script usb_modeswitch_dispatcher which is launched by the udev daemon.
Note that usb_modeswitch itself has no specific Linux dependencies.
This manual page was originally written by Didier Raboud (firstname.lastname@example.org) for the Debian system. Additions made by Josua Dietze. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU General Public License, Version 2 or any later version published by the Free Software Foundation.
The complete text of the current GNU General Public License can be found in http://www.gnu.org/licenses/gpl.txt