The reason port forwarding is necessary is because of NAT. The address on the outside of the router is in a different network from the addresses on the inside of the router. That means that when someone connects to your server using the outside IP address, in order for that traffic to reach your server which actually has an address on the inside of the router, the router has to know how to translate the destination IP address. So you tell the router that when it gets traffic on the outside IP on port 1234, it should send it to the inside IP where your server is. Otherwise the router has no idea what to do with the traffic, because it has already reached its destination, which is the outside IP address.
Now in your case, I know nothing about your cellular network, but there are basically two possibilities. Or maybe three.
Either there is no NAT, in which case there is no need for port forwarding. Or there is NAT, and it is on a router that you can't control, so you're boned.
The third possibility is that there is no NAT, so you don't need to port forward, but the ports you will need to use are still firewalled somewhere. Or the instability of your connection and IP address assignment will get in the way of running a server well.
I recommend a cheap VPS instead.
Now in your case, I know nothing about your cellular network, but there are basically two possibilities. Or maybe three.
Either there is no NAT, in which case there is no need for port forwarding. Or there is NAT, and it is on a router that you can't control, so you're boned.
The third possibility is that there is no NAT, so you don't need to port forward, but the ports you will need to use are still firewalled somewhere. Or the instability of your connection and IP address assignment will get in the way of running a server well.
I recommend a cheap VPS instead.