This is pretty straightforward, the local carrier I'm with (Vodacom SA) has been offering it for years under the 'Look4Me' brand-name. Essentially it relies no

This is pretty straightforward, the local carrier I'm with (Vodacom SA) has been offering it for years under the 'Look4Me' brand-name. Essentially it relies not on the phone itself but on the carrier's network infrastructure. In terms of GSM, with which I am more familiar than CDMA, a mobile phone 'registers' with any GSM tower and passes along certain parameters. Using that information, the carrier can combined the input from one or more towers to triangulate the location of the phone. The process is opt-in and used via control codes. For instance typing in 120888*phone number# sends a request for the location of that number. If they have not agreed to be tracked, they are sent an SMS showing them the phone number of whoever sent the request and asking them if they want to be tracked. If they ignore the SMS, nothing further happens. However, tower triangulation is inherently inaccurate and in general accuracies are only within about 100 m at best and valid for the past 10 minutes. It's definitely nothing close to the kind of accuracy that solutions which use GPS, such as Apple's Find My Phone, can give you.