For many user of the tracker may like this usage which is so easy. Only install the tracker into the car, user could control and locate the car with cell phone.
What he needs to do is to send one short message. So many car owner like this, but only not perfect is that the position information is coordinates. To many people, the coordinates are only numbers and meaningless. User could look this coordinates with Google earth or Google map. In all, this is simplest usage of the tracker.

Real-Time GPS tracking systems update about every 1 minutes so users can see the vehicles "current" location. Live tracking helps with dispatching, on-time service and remote vehicle tracking.

Solution I Tracker, Cell phone private cars, SMS
Solution II racker, modem, PC, software, small groups about 50 vehciles, SMS
Solution III Tracker, modem, PC, software, small groups about 50 vehciles, SMS/GPRS
Solution IV Tracker, server, software, big group more than 1000, like TAXI, BUS, GPRS
Solution V Tracker, server, software, large group, all kinds of vehciles, GPRS