Modem is not being detected (Why I've to usb_modeswitch?)

Try udev rule wich launch a script every time you plug the modem.

ACTION=="add", ATTRS{idVendor}=="XXXX", ATTRS{idProduct}=="UUUU", RUN+="/home/user/script.sh"

Replace XXXX and UUUU with vendor and id product,put rule in /etc/udev/rules.d/99-yourrule.rules and reboot or restart udev. Must work