I tried Sprint Navigation, as well as AT&T Navigator and VZ Navigator, on BlackBerry Curve handsets. All three are very accurate, and can lead you to your destination with little fuss.
Keep in mind that the functionality of a cell phone GPS application can vary depending on the phone's capabilities; on a small, standard handset, the app might not be able to do all of the same things that it can on a BlackBerry. In addition, a great deal of the GPS functions are dependent on your cell carrier's network, so you won't be able to take advantage of them if you're out of range of a cell tower.
One nice touch: Both Sprint Navigation and AT&T Navigator allow you to call a toll-free number and speak your destination address. Unfortunately, Sprint then requires you to navigate to another screen to prompt the GPS to direct you to the location.
Sprint Navigation includes a freebie TeleNav Maps tool. It's similar to Google Maps--you can get written directions, but without GPS assistance.
gives you only a one-day free trial (AT&T offers a 30-day trial). You might be able to grab a 30-day trial through TeleNav's site, however.