Just been reading through this thread with a bit of interest.
I'm not looking to fit a tracker simply because if the car gets stolen, then the insurance people can cough up, as for the car I wouldnt want it back anyway.
However an ex work collegue , who's into all things techy has fitted some sort of gadget to his car that is permantly hard wired and shows it's whereabouts on his iphone, or an apt on his iphone, like I say he's the techy one not me.
I do know though that he bought this thingy on the net and fitted it himself and at no great cost, I'm not sure how accurate this thing is but it sounds very much like what paul141 is talking about, and it showed if and where the car was parked up, or moving and in what direction.
I will try and get back in touch with this fella and put up any info that I can.