Data Dongle or tethered phone for remote MQTT ?

[affinite]

Hi all
I want to setup a mobile/GSM data connection so that I can remotely monitor my boat. 
I've setup the MQTT stuff on the Pi and I can monitor it when the Pi is connected to a WiFi network but I now want to connect the Pi to the internet using GSM 3G or 4G.
I have a Vodafone/Huawei K4203 dongle and a number of old phones which I could use but have no idea how to connect/set them up on Raspbian/Linux/OpenPlotter
Bye the way, I am in the UK and the boat is in Greece

So ... if you have this sort of connection setup Id be very interested to hear how you set it up. 

Thanks
Steve