Most phones come with GPS these days. Even if they don't have GPS they can be tracked to a "rough" location based on cell tower.
There is software/service that is readily available.
Some service providers, IIRC ATT being one of them do offer the service for phones that support the feature.
The one consistent factor for the consumer is you need to get your hands on the device to either install software or enable the service.
http://www.accutracking.com/