To see how they stacked up, I tried all three apps on BlackBerry Curves, and I found that they all worked as promised--mostly. They weren't identical, however, and though I'm not ready to give up my Garmin Nuvi, I'd recommend AT&T Navigator to anyone who wants to use their phone as a navigation system.

Got a GPS?

I'll tell you right away: I'm in love with dedicated GPS navigation devices, and I'm spoiled. I've tried lots of them, and I'm hooked on Garmin's Nuvi 760, a $350 handheld GPS device that I wouldn't give up on a bet. (See "Notes From the Road: Wi-Fi Tips, Garmin GPS Test Run" for more details.)

On top of that, my wife, Judy, is a top-notch map reader (and like most GPSs, she can change her voice and do a great London accent). So when PC World asked me to try a few more--and said they'd pay me to do it--I jumped.

Besides, I was mighty curious to see how usable GPS navigational tools are when packaged on a handset. The quick answer: They're very accurate, and wonderfully handy. They'll create a route and get you to your destination with minimal hassle; they'll also find you a Starbucks and give you voice and on-screen turn-by-turn directions.

All three services have one significant limitation, though--and I'll talk more about that in a minute.

Leveling the GPS Playing Field

To level the playing field, I tried finding my way around town using one of the best handsets available for GPS navigation, the BlackBerry Curve. I received BlackBerry Curve loaners from three wireless vendors with their branded GPS tools, and played with them for a month.

Verizon sent me one with its VZ Navigator, which uses Networks in Motion for its GPS application. AT&T Navigator is powered by TeleNav; ditto for Sprint Navigation. But while the AT&T and Sprint apps offer similar interfaces, AT&T's has features missing in the Sprint version. All three services charge $10 a month or $3 a day, exclusive of data charges (more on that later).

Of course, I would have liked to include something from T-Mobile, but that company is the only major national carrier that doesn't offer its own branded GPS app.