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If you need to find cell phone user's particular location (even if it's your own), you can use GPS. GPS stands for "global positioning system," and it was originally developed by the United States Department of Defence for their use. GPS uses a GPS receiver; the receiver calculates the user's position by precisely timing signals that are being sent by GPS satellites that are in orbit above the earth.

Increasingly, cell phone handsets include GPS as one of their functions. However, some older handsets don't have this function, and it can be difficult to find users by location. One way around this, is by using cell phone towers to find a particular cell phone user.

You can do this by using a process called "triangulation." It uses the cell towers that cell phones, GSM terminals, and GSM modems to use. In fact, iPhones use WiFi data and the triangulation method to locate iPhone users on Google maps (along with GPS on the newer 3G handsets).

There are also commercial locating services such as FollowUs; with these, you pay to locate handsets that don't already have GPS included. If you are a developer, you can also use commercial services such as Skyhook and Navizon.

Besides using commercial services, you may also be able to collect cell IDs yourself with GSM or GPS capable equipment. You would store this data in a database and then later, you'd use it to find out where handset users are, by first retrieving the list of cell ids they are close to, then finding these in your own database and resolving them to a latitude / longitude that was recorded when the cell id was added to the database in the first place from a device that did have GPS available.

There are several open source resources with cell ID location data available. Some of these are: CellSpotting; OpenCellID, 8Motions; ZoneTag Cell Location API, Yahoo.

OpenCellID may be especially useful, since it's an open-source database of cell IDs where you can create your own application to gather information about particular cell locations (as in the database described above). Because each cell phone user has a unique number for his or her own GSM cell, this can help you find the exact operator. If you know the number and you know the cell, AND you know the position of the cell (by using triangulation), you can find the user. It's not quite accurate, since a given cell can cover from several hundred to several thousand meters, but it's quite a specific locator nonetheless. It can at least help you narrow down where someone is if you need to find them.

Again, as older handsets are retired and new handsets are used, most of these will have global positioning system capability included. This will make the aforementioned methods and applications less necessary, if not obsolete. However, that may be a few years and it's also quite possible that more "frugal" cell phone users will use their old handsets until they simply can't function anymore. Therefore, until everyone is on a cell phone with GPS capability, it's useful to know that there are ways to find users as you need to, even if it means you have to use a little bit of old-fashioned elbow grease.