The cars factory GPS is only a receiver, so it can't send a message to you (although it may be able to log trips*), so you would need to install a GPS tracker, this device has a GPS receiver and a cell phone and can be set up so that you can call it and find it's location, it can also be set up so that if it moves from it's present location it can alert you with a phone call.
There are a few thing you need to conciser :-
1) If the car is in a garage it won't get a GPS signal, so if you call it in the garage it won't tell you where it is.
2) For the tracker to call you when it is moved, it would need time to get it's location from visible satellites and work out it has moved a certain distance away from the garage, before calling you
3) The tracker will need external power from the car's battery, they do have built-in batteries but it won't last for 6 months
* Alternatively you could fit a GPS logger, this device will store any new locations in it's memory so that you can check it at a later date (i.e.when you get the car back), It would probably also need powering from the car for it to last over the summer