I have an internal Mobile Broadband network card on my laptop but the network manager does not pick it up. I only see WIred and Wireless.
There is currently an open issue on GitHub about this and I have just recently got a Mobile Broadband device to do some development and testing so I can hopefully get this feature implemented.
However, in the mean time, you may still be able to configure your card by doing the following:
Settings -> Network -> Edit Connections (at the bottom) -> Add -> Mobile Broadband
If your device has been detected and has drivers, you should be able to configure it following those menus.