Sprint has a nifty feature called Sprint Family Locator, and it allows account holders to monitor the real-time location of family members by tracking their phone's Global Positioning System (GPS) system.
Visit "sfl.sprintpcs.com" to sign up for Sprint Family Locator service. Enter the primary telephone number on your Sprint account and choose your billing method. The first 15 days are free; as of October 2009, the service is $5 per month thereafter.
Sign in to your account using your telephone number and the password you created. Click on the telephone on your account you want to track.
Wait for the locator service to pinpoint the location of the phone. You can click "Refresh" to monitor the phone's location as many times in a day as you want.