Firstly plug the device into a Windows machine (after having installed the drivers) and check to see if you can see the serial ports. If you can then the unit is setup correctly, if not it is in MBIM mode only and you need to check out https://forum.sierrawireless.com/viewtopic.php?f=117&t=8863&start=15#p37212.
Assuming the prots do come up I would STRONGLY recommend deleting every instance of the open source QMI interfaces from the system, I have seen instances recently where the unit was configured correctly and
You need to do the following
sudo modprobe -r qmi_wwan
rm /lib/modules/$kenel/drivers/usbserial/qcserial.ko
there is also going to be qmi_wwan.ko file around somewhere (may well be the same path as above) , you need to find it and delete it as well. After this reboot.
Install the GobiSerial and GobiNet devices then plug the unit in after that you should be able to see the /dev/ttyUSB’s and /dev/qcqmi interfaces.
Regards
Matt