Microcontroller information transfer to Android application
For remote tracking of a car over a wide area, the only practical solution is a cellular modem. Gsm or cdma modules are available. They require service via a cellular provider.

Honestly, the proliferation of cheap (under 25 on sale) android cellphones provide all you need for this. Each one is cheaper than most cellular modules (let alone combined with gps and microcontroller costs), provide battery backup, multiple debugging interfaces (lcd, usb, wifi), have gps, standard power connector, etc. And can be easily programmed. And allow a level of abstraction from the specific hardware as most simple android app code around gps does not need porting.

At that point, in either case, they speak with a web server on your end. And both require not much signal/bandwidth to work. With prepaid cell services you could be talking cents a day per device service wise.