Originally Posted by pintycar
Hmmm that's weird. I can't remember from the top of my head. I'll check it out tonight and make some screenshots of how things look.
Not to worry, I got it working
To be honest I have no idea what I did to get it working as everything I did I had already previously tried. However, for the sake of rounding off the thread (should others have the same issue) here is the exact settings that I am using.
Firmware Version - 18.104.22.168.374_720
In Advanced WAN: Dual WAN
Enable Dual WAN - On
Primary WAN - WAN
Secondary WAN - USB
Dual WAN mode - Fail Over (This simply means it'll always use the Primary when it can, should your internet go down it'll switch)
In Advanced WAN: Internet Connection
WAN Type - USB
Enable USB Modem - Yes
Location - Manual
USB Modem - WCDMA(UMTS)
Everything else is blank other than USB Adapter which is set to Auto.
Once you have your setup configured as above simply plug your phone into one of the USB ports (I use the top one if your router is lying down) and enable "USB Tethering".
If everything is working you SHOULD see Primary WAN - Connected and Secondary WAN - Standby.
When your Primary WAN (cable for example) goes down, it switches to your Secondary WAN which will then change to Primary WAN - Disconnected and Secondary WAN - Connected.
Easy way to test it out is to simply unplug your WAN cable, it should automatically switch to your phone.