First of all, I want to apologize for adding to this old thread, but I have found a strange solution which might help someone.
If your modem is showing up as USB but LTE interface is not showing up:
1) Try upgrading firmware and ROS.
2) Try reset.
3) Connect your phone and share the Internet using USB tethering, if LTE interface shows up for the phone then disconnect the phone and connect your modem, it should show up.
Tested with Huawei E398, no luck.
According to this thread, viewtopic.php?t=60675
there will not be any support for this modem. Set it up as a PPP-client using port:usb. Make sure to set data and info on separate channels so you can get the signal strength and other info without being forced to terminate the connection every time.