"What I don't understand here is how the mobile device finds the remote
server under that network address. It looks as if your gretl server is
also the network node (Wifi sharing at home? DHCP?), or how's your setup?
So what would be very interesting in practice is whether this broadway
transmission also works on a "really" remote server."

This is a "really" remote server :)

Is going to be a long explanation :) and all informations are on an Ubuntu 13.10 with a dynamic IP from the ISP and a wifi router (DHCP)

-usually the ip from the internet provider is dynamic, in order to connect to my server I use http://no-ip.com/ service which depending on the settings updates the ip address every half an hours (or even 5 minutes it depends on the user settings), so the ip address is something like this username@no-ip.org 

- the router gives dynamic ip to the laptop/desktop/server so I have a local fix ip see  http://ubuntuforums.org/showpost.php?p=11961133&postcount=2 , also in order to have a secure connections all ports are closed except 22 and 80, and the router has port forward from 22 to the server. (router port forward depends on the models so I'm not going into specifics)

- on the android tablet/phone I use connectbot with port forward enabled 

nickname : usernick

type: local

source port:8080
destination: localhost:8080

So I'm using connectbot to connect to my server, with the port forwards on. The information goes through the ssh connection to the server and the port forward redirects all connection from port 80 to the server localhost. So actually in the web browser we are seeing the server localhost, which thanks to the GTK3 is Gretl.

I've tested and everything works great: opening new data, saving data, saving session, keyboard shortcuts, scripting, etc.