Cell phone companies can approximate your cell phone location by "pinging" it. When cell phones are turned on, they emit a signal. Cell phone companies can "ping" or contact the cell phone and discover the nearest tower the signal is coming from. Police and law enforcement use this method regularly to track down missing persons. It's illegal to access phone records for a cell phone you don't own, but you can ask your carrier to help you ping your own number.
Call 911 and file a police report for the phone if it's been stolen, or is on a missing person. The police can legally ping your cell phone for information in a criminal investigation.
Ask your cell phone company to ping the phone for you. Companies have different policies regarding how and when they will ping your cell phone, but they'll need you to verify personal information and prove you are the owner of the account.
Enrol in a tracking program offered by your cell phone company if you have lost the phone and there is no legal issue demanding a ping. For instance, Nextel offers a Mobile Locator service that allows you to request cell phone pings.
Order a ping from a third-party service. Be careful only to use this option if the cell is registered in your name; otherwise you may be breaking privacy laws. Private services require fees.
Use the GPS capabilities of your cell to track the phone. While pinging is possible only when the phone is turned on, the cell phone company can track a GPS signal even with the cell turned off.