Not all cell phones have GPS tracking chips. The only ones that have tracking chips are the smart phones, such as an iphone.

Yes, there are several phone tracking services available for cell phones.

There are specific phones that use cell phone tracking, not all use such a feature. Some older phones are not able to be tracked, and some phones only allow tracking by 911 calls.

GPS cell phone tracking can be used for many things. One benefit is map applications on cell phones. Without GPS this would not be possible. GPS can also be used for certain games using location such as geocaching. GPS can be used to locate cell phones in case of emergency. If one calls the police but can't verbalize the location due to the circumstances then the police can track the cell phone's GPS and rescue the person.

Yes, AT&T offers cell phone GPS tracking through their FamilyMaps service plan. This is available with all cell phones, however its information is more accurate with GPS phones.