Nobody likes a backseat driver, but a mobile phone that gives driving directions could come in handy, especially for business travelers and for tourists visiting unfamiliar territory. Televigation's new TeleNav service provides directions across the continental United States and Hawaii. The service has great potential, but it's too glitchy to recommend for now.

TeleNav requires a Nextel phone with GPS and a subscription to Nextel's Total Connect data plan (the TeleNav service adds $10 a month to the plan price). Nextel's cellular network enables the service, so if you don't have a signal, the GPS can't find you and can't give you directions.

I tried out TeleNav using Nextel's i730 phone in Los Angeles and in the San Francisco Bay Area. There are three ways to input locations for which you want directions: Dictate your destination address into the phone, type it in via the keypad, or access the service via a Web-connected computer first.

TeleNav's voice recognition method sounds convenient, but the service often didn't understand the street names I dictated. And typing in an address using the dial pad was even more cumbersome, not to mention time-consuming. Accessing the service by PC in advance requires more planning, but it's also the most straightforward method, and it worked the best.

TeleNav has BizFinder for locating businesses, too, but I found the yellow-page information terribly outdated. Despite such hang-ups, once I provided my destination address, TeleNav's mapping database was usually good enough to get me there with turn-by-turn instructions. The most helpful part: If I missed a turn, TeleNav recognized that I had gone off-route and offered to reroute me with a fresh set of directions.

Televigation's TeleNav service still has too many rough edges at the moment, but with some work this phone-based navigation tool could become a real travel aid.