I've got a friend who runs a local business in my suburb.  Recently he switched to 4G wireless broadband at his shop and since then he's been unable to access a system remotely that runs internally in the shop.  I figured it would need a NAT rule and sure enough there is a specific port to access the system.

I told him this and he went off and entered a rule in his router but it still wasn't working.  When I went in this morning and had a look I could see it all looked correct to me.  But when I tried browsing to the service from my mobile using the external IP and port it wouldn't resolve.

It's a Huawei B315 LTE modem.  Does anyone know of any issues forwarding ports on this device or type of broadband service?