I use a USB-Modem to connect to my PC to the Internet. But every time I connect it via USB, I have to enable mobile broadband via the networking applet on the task bar. I know it's not much work to do but i want it enabled by default so that it'll connect to the Internet automatically.
Try adding this command to your start-up-scripts
nmcli nm wwan on
or make a longer script, if you want it to sleep before executing, like here: longer answer
Longer answer working link below: https://bugs.launchpad.net/ubuntu/+source/modemmanager/+bug/874900