Kansas City, Mo. ? The growth of cell phones with global-positioning technology is making life uncertain for the makers of personal navigational devices that help drivers figure out where they are and where to go.

Manufacturers of standalone GPS products must move quickly to transform their dumb map readers into intelligent devices that can provide a host of services such as traffic avoidance.

Otherwise Garmin –which is based in the Cayman Islands but has its headquarters in Olathe, Kan. — TomTom and other makers of satellite navigational devices risk obsolescence in a future in which customers view navigation as simply one more application for their phones.

Manufacturers already have begun broadening their GPS products, adding wireless technology to some of their top-end devices to provide up-to-the-minute traffic data, nearby gas prices and weather information. Research firm Berg Insight estimates that more than 80 percent of navigational devices will have wireless capability by 2015.

Other products, particularly pricey units built into a vehicle’s dashboard, can play digital audio files or act as an Internet hub for the driver and passengers.

These features could give manufacturers new revenue streams with monthly subscription fees, which they don’t currently charge.

Although the economic slowdown has hampered sales somewhat, satellite navigation devices are still popular. NPD Group says U.S. sales are up 4 percent to 4.7 million through September from the same nine months in 2008.