[tyingq]

Here's what it sounds like. Most of these types of devices (USB/3G) are "multimode" devices. That is, they can act like either USB storage or a USB 3G/4G device. On Windows, that's handy because it can come up as storage and then the end user can install the drivers right from the device, and the drivers then handle the "mode switching" from storage to 3G/4G-device. It's basically a way to bootstrap operation without requiring driver downloads.

This "usb_modeswitch" program handles that for linux. It sniffs the USB traffic and switches the mode to 3G/4G for you. All the crazy args are whatever was in the Windows config file. The -v 12d1 is the "VID" (vendor ID) of the device to sniff traffic for. The -p arg is similar, but the "PID" (product ID). The -P 14ac is the "PID" to switch to to get from storage to 3G/4G device. The -M <long-string> is the magic payload sent to the device to make it switch.

[ajsnigrutin]

It has to be said here, that usb_modeswitch software already recognises most modems and has those magic strings saved in a file, and does the switch automagically.

Only if you have a relatively new or rare modem, you need to find the magic string yourself (or even reverse engineer it from a windows setup), to make it work.