Does anybody know of/have experience of a UK-available mobile-data-dongle&provider that will work with Linux of course ... with the following crucially important feature(s): I want to purchase credit and "activate" the device only very occasionally but I will not have access to the physical dongle when I do this. The providers that I've checked so far (TMobile and Three) require the dongle to be the connecting device at the point of service-purchase - this won't work for me.
To explain a little more for those of you that have read this far: the plan is for it to go with my Raspberry Pi + GPS dongle into my car. When someone nicks the car, I want to able to enable the data-dongle remotely (I assume this will involve punching my IMEI and/or mobile number + credit card number into the mobile-service-provider's website) whereupon the periodic attempt by the RPi to establish a VPN into my home machine will suddenly magically work, and I will be able to connect back into the car's gpsd and hotfoot it after the criminals with my baseball bat in hand. I'm too cheap to buy a full-time data connection, hence this question.
Any thoughts most gratefully received.