Question: you have an emergency while on the road and call 911 from your cell phone; do you have to give your location to the operator or can he locate you automatically? Answer: if your cell phone has been manufactured after 2005, he can almost certainly locate you automatically thanks to a FCC rule that went completely into effect at the end of '05.

The directive, called E911 (short for Enhanced 911), mandates that all new cell phones support location identification technology, meaning that when you dial 911 from your mobile, the public safety answering point (PSAP) can locate you as accurately as within 60 yards of where you are. The main technology that makes this possible is GPS--or Global Positioning System.

How GPS Technology Works

Essentially, GPS technology works this way. Your cell phone emits radio waves that are picked up by orbiting satellites. It takes three satellites to work together to locate the handset, using a geometric technique called trilateration: the phone's waves create a spherical signal around each of the three satellites, and where these spheres intersect on the ground is the location of the cell phone.

Besides this important role in helping locate wireless 911 callers, GPS technology has some great commercial applications when linked to cell phones. So, although practically all new phones have basic location identification technology that satisfies the E911 directive, some known as GPS phones include advanced features that give the user some unique benefits.

GPS Cell Phone Applications

One of the most popular application of GPS phones is providing the user with turn-by-turn driving directions--both in the form of spoken pre-recorded indications and in the form of a map on the phone's screen. Until a few years ago, this technology was only available on luxury cars (remember the movie The Out-of-Towners?); now, it is as inexpensive and convenient as a GPS phone and a plan that supports it. Some of these services have become so advanced that when you miss a turn, the phone instantly finds the next best route to your destination and takes you from there.

A GPS phone can also be a viable all-in-one tool in the hands of a hiker or outdoors person who can know exactly where he is without the traditional aid of a map and compass. The only caveat is that in order for the GPS service to work, the phone must be physically located within the carrier's service area--in other words, if you are lost in the wilderness and your phone doesn't have a signal, you better have that old-fashioned map and compass as a backup, or it's al fresco time.

Also, many parents are finding GPS technology to be a convenient and non-interfering way to keep tabs on their kids' whereabouts. For instance, Sprint's Family Locator Service uses GPS technology to locate the kid's phone and give parents the location information both in map and text format on their own handset--as long as both phones are GPS enabled.

How Much GPS Cell Phone Service Costs

So what does it take to have this service? The two essential things you need are a GPS-enabled cell phone and a service that supports it. Although practically all new phones now have the basic E911 location identification feature, only a few models are fully GPS enabled. Nextel was the first wireless carrier offering GPS-enabled cell phones, featuring either the TeleNav (Telenavigation) or the ViaMoto (Motorola) GPS systems. And as far as carriers, Sprint and Nextel are the ones who broke new ground by offering plans that include GPS services. Nextel is now running some interesting cell phone deals also on phones featuring GPS technology.

If this technology sounds interesting to you, typical cost (beyond your regular cell phone service) is within $10 a month, which is not a lot considering the great benefits you get from it.