I tested AT&T Navigator, along with Sprint Navigation and VZ Navigator, on BlackBerry Curve handsets. All of these apps and services are very accurate, and give driving directions with minimal hassle.

Note that a cell phone GPS application offers varying functions depending on your phone's capabilities; on a regular clamshell, the app might not be as full-featured as it is on a BlackBerry. Remember too that such applications' GPS functions rely on your cell carrier's network, so you won't be able to play with them if you're headed off-road and out of range.

AT&T uses the GSM family of network technologies, so its navigation application is much more useful when you travel abroad, with service in over 16 countries in Europe as well as parts of Canada, China, and Mexico.

Another neat feature: Both AT&T Navigator and Sprint Navigation let you call a toll-free number and speak an address. The AT&T application promptly delivers voice directions in response.

Like Sprint, AT&T bundles the freebie TeleNav Maps tool on its BlackBerry devices. You can try AT&T Navigator for 30 days without charge, a nice touch. Once you subscribe, the cost is the same as for other carriers' GPS navigation services: US$3 per day or $10 per month. For details, go to the AT&T Navigator site, but turn down your PC's speaker volume first--the site has a chatty and lengthy Flash-animation pitch.