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 , which uses for its GPS application. is powered by ; ditto for . 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 , but that company is the only major national carrier that doesn't offer its own branded GPS app.