NEW YORK - With instant messaging programs, it's easy to tell whether a friend is at the computer, ready to chat. Despite its immense popularity, the concept of the buddy list hasn't made a smooth transition to the mobile world.

Now a small cell phone provider named Helio LLC is introducing a service for its youthful target audience that not only lets you know whether a friend's phone is turned on, but tells you where that person is.

The new "Buddy Beacon" feature uses GPS satellite technology to track up to 25 fellow Helio subscribers. Their locations are plotted on a map displayed on the screen of a pricey new handset that's also being launched on Thursday.

The user can see the nearest address for each buddy's location. If one user notices that a friend is nearby, a call can be placed directly from the application. As you might expect, a person has to consent to being tracked on someone else's list of Beacon buddies.

The telecommunications bubble of the late 1990s included countless unfulfilled promises about the impending arrival of cell phones with robust location-tracking capabilities.

A service similar to Helio's was once available through the former AT&T Wireless, but disappeared with that company's acquisition by Cingular Wireless two years ago. Rather than GPS, the "Find Friends" service relied on triangulation to locate a subscriber, measuring the distances a signal was traveling between the person's phone and the closest network antennas.

More recently, companies including Sprint Nextel Corp. and Disney Mobile have introduced phones that enable parents to track the location of a child. Likewise, a growing number of cell providers are offering tracking services for businesses, particularly those with fleets of vehicles.

As with other Helio non-voice features, there's no extra charge for using the Beacon application beyond the premium price tag for the company's calling plans, ranging from $65 to $135 per month. Likewise, as with Helio's other high-end handsets, the new "Drift" phone featuring the Beacon service is priced at $225.