hi there,
navman do a system, that you can lease or buy, and then a subscription.
there are a lot of advantages to them.
you can monitor the vehicles from any pc, and gives you an amazing amount of info, it will even tell you if the vehicle is being moved and the engine hasnt been started. you can then configure your email to send that info to your mobile.
another use is that you can prove to the tax man, that the vehicle is only ever used for business miles or not as the case maybe.
regards
martin