usb_modeswitch: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/usb_modeswitch - from package: usb-modeswitch

You may install the required package with command apt-get install {package}
Error in other languages:
usb_modeswitch: bevel nie gevind nie
usb_modeswitch: comandă negăsită
usb_modeswitch: comando não encontrado
usb_modeswitch: commande introuvable
usb_modeswitch: command not found
usb_modeswitch: käsku ei ole
usb_modeswitch: không tìm thấy lệnh
usb_modeswitch: komanda nerasta
usb_modeswitch: Kommando nicht gefunden.
usb_modeswitch: kommandot finns inte
usb_modeswitch: komut yok
usb_modeswitch: nie znaleziono polecenia
usb_modeswitch: níor aimsíodh an t-ordú
usb_modeswitch: no se encontró la orden
usb_modeswitch: no s'ha trobat l'ordre
usb_modeswitch: opdracht niet gevonden
usb_modeswitch: parancs nem található
usb_modeswitch: perintah tidak ditemukan
usb_modeswitch: príkaz nenájdený
usb_modeswitch: příkaz nenalezen
usb_modeswitch: команда не найдена
usb_modeswitch: командата не е открита
usb_modeswitch: 命令找不到
usb_modeswitch: コマンドが見つかりません