Available in Czech Republic, too, 98 grams, and pretty cheap. On my Nokia n900, GSM parts died, and hacking cellphone you are using is a bad idea... So... what about Pixi? Underpowered hardware, but still more powerful than n900. Does firefox os support wifi tethering by default? Is it reasonably easy to hack? (I guess "apt-get install python would be too much to ask, but..) Other candidates are Jolla/Sailfish and Ubuntu Phone.