On Sat, 26 Jun 2004, Major Variola (ret) wrote:
Eventually the cellphones will be able to tell another phone approx where they are. [...] The marketing reason would be to help people find others geographically.
At least with GSM, the base station always knows the approximate distance to the phone (this is needed by the GSM protocol, for reasons related to time slot management in the presence of finite speed of light, but it might be possible to hack the phone's firmware to fool it, or to register with fewer base stations than usual). The GSM network's database knows the exact locations of all the base stations. Add a little software to do triangulation from multiple base stations, and the GSM network knows the location of the phone, to an accuracy that depends chiefly on the base station density. Add a layer of user interface software, and you're done. No cooperation from the phone is necessary, except what the phone would normally do in order to register itself with base stations so that it can receive calls. No GPS or other non-GSM protocols are necessary. This is already offered as an extra cost service (branded "Look for me") by Vodacom in South Africa. It's targeted at parents who want to know where their children are, and the phrase "with their permission" is included in current advertising. As the seeker, you send an SMS (text message) to a special number to "register" your phone as a user of the locator service, and to ask for the location of another phone. The network sends a message to the target phone, and the user must reply to give permission to be located. Then the network sends a text message to the seeker, telling them the location of the target. I don't know whether the target's permission is asked every time, or just once per seeker; I do know that it's not just once globally. In any case, the "permission" is just a flag in a database, and is not really needed by anybody with back-door access to the GSM provider. --apb (Alan Barrett)