If you go download from the USB-ModeSwitch site,
http://www.draisberghof.de/usb_modeswitch, you can follow the instructions given there to install it.
Hope this helps some.
[edit]
You may -- may -- be able to find
usb_modeswitch in
apt-get (underscore not dash)? The current stable version is
usb-modeswitch-1.1.6 (the name of the download file at the web site).
[/edit]