Works perfectly once it has been switched into modem mode using USB_ModeSwitch. Note that this changes the USB vendor/product IDs to 0421:062D.
Instructions for Trisquel 7.0
apt-get install usb-modeswitch usb-modeswitch-data
Extract the file "0421:062c" from /usr/share/usb_modeswitch/configPack.tar.gz or
download it from GitHub:
wget https://raw.githubusercontent.com/digidietze/usb-modeswitch-data/master/usb_modeswitch.d/0421%3A062c
Switch the Nokia CS-19 into modem mode (requires root):
usb_modeswitch -v 0421 -p 062c -c 0421\:062c
At this point, you might be asked to enter your SIM card PIN.
You should now be able to
set up a mobile broadband connection using NetworkManager.