Why pay $2,000 for built-in car navigation when everyone's cell phone already has it—or will shortly? Each cellular carrier now has at least one available navigation service. The latest entry is the Sprint network, which teamed up with AAA and Networks in Motion for a $10-a-month service called AAA Mobile.

A year ago, navigation was available on a handful of higher-end phones. Now it's a feature on an increasing number of phones, including even some free-with-a-service-contract phones, because carriers find navigation-service subscribers are less fickle than those downloading music or videos. And most phones have embedded GPS chips, so there's no additional manufacturing cost. Sprint subscribers who opt for AAA Mobile can download the software.

The AAA Mobile services rides atop location-based services created by Networks in Motion and also used on the Verizon network, where it's called VZ Navigator. What AAA adds to NIM's package is the AAA map package, AAA diamond ratings for hotels and restaurants, and points of interest from the AAA guidebooks.

You don't have to be an AAA member to subscribe to AAA Mobile. But if you are, you can call for help (tow trucks and jump starts, for example) with a single button press on your phone. If any AAA member registers his cell phone number, AAA says, it will be linked to his member number. Then when you call for help, both should be forwarded to the AAA call center, potentially reducing some of the hassles of keying in a member number and waiting for a live operator to pick up.

The service runs $9.99 a month. Alas, AAA members who flash their member cards at the Sprint store don't get a discount. Unlike with VZ Navigator, AAA Mobile has no $3-a-day plan for occasional users who want the service for a weekend trip, then don't need it again for a month or two. Sprint has an exclusive with AAA Mobile, although it's expected to be offered on other carriers in the future.