Comment 1 for bug 1337542

"Jul 3 23:44:31 usb_modeswitch: switch device 12d1:14fe on 003/005"

usb_modeswitch has found the dongle in initial mode 12d1:14fe and has switched it into modem mode

"Jul 3 23:44:32 kernel: [19565.429763] usb 3-1: New USB device found, idVendor=12d1, idProduct=1506"

"Jul 3 23:44:33 usb_modeswitch[16596]: usb_modeswitch: switched to 12d1:1506 on 3/6"

The first indication of a problem is here:

"Jul 3 23:44:34 usb_modeswitch[16596]: usb_modeswitch: add device ID 12d1:1506 to driver option"

The option driver did not attach by itself to the dongle, usb_modeswitch will check for that and load the driver using the new_id function of the driver if no driver claimed the interfaces.
The new_id function can not distinguish between serial interfaces and net interfaces so it will erroneosly also bind to the net interface:

"Jul 3 23:44:35 ModemManager[812]: <warn> (ttyUSB1): port attributes not fully set"

The reason for the driver not binding by itself (and excluding the net interface) is most likely due to an outdated option driver in your distro, a driver not directly supporting your dongle.

Please attach the output from lsusb -v -d 12d1:1506 so I can see the interface attributes in order to tell if the device is supported in mainline linux kernel.