I live in a remote location where there is 4G but no other internet.
I’ve got "Android Phone" working as my Primary (and only WAN) on AC86U and had it working well on AC68U before I upgraded. I've used it exclusively for about 6 months and it is pretty stable - much more than I expected. The entire set up is done with the web interface but it is not very intuitive.
I bought a cheap Android phone especially for the purpose. I researched quite a bit as the modem in the phone can be a limiting factor on the speed of your connection. The phone I use is a Umidigi A3X which I got on Amazon for under 80 euros. It runs a stock Android 10. I have not upgraded the phone in any way. Within the phone’s data and internet settings, there is "USB tethering" but this cannot be turned on till the router is set up, connected and waiting for a connection.
I have a 4G sim from the Spanish provider Lowi which is part of Vodafone and uses the Vodafone network.
On the router (having first applied the latest Asuswrt-Merlin firmware, I took these steps:-
1. Plug in the Android phone, I have it in USB 2.0 socket and use the cable that came with the phone.
2. USB application menu, 3G/4G, "Internet Connection" tab, switch on, select Android phone from the drop down and apply.
3. Dual WAN tab, "enable dual WAN" to off, "Primary WAN" select "USB" and apply.
4. Switch on USB tethering in Android phone settings. There is a short wait while it finds the connection.
A reboot might be needed between 3 and 4. Sometimes you need to switch on "USB tethering" on the phone again after a reboot, and sometimes not - not sure why.
The network has the WAN IP passed by the Android phone and uses the ISP’s DNS, which I would like to change but haven't yet worked out how.
Also, on the WAN > Internet Connection page, there are two settings under “Special Requirement from ISP” being “Extend the TTL value” and “Spoof LAN TTL value”. Does anyone know what these two values do?