MapQuest recently released its own free voice navigation app for the iPhone and BlackBerry.
From the website: “The MapQuest 4 Mobile downloadable application provides easy access to Directions, Maps, and Local Search. With MapQuest 4 Mobile you also have the ability to integrate your saved maps and directions on MapQuest.com to the MapQuest 4 Mobile mobile application. To start saving your maps and directions generated at MapQuest.com”
Mapquest 4 Mobile
Via Lifehacker: MapQuest 4 Mobile features voice guidance, off-route assistance (it can automatically re-route you), point-of-interest integration, and plain-text search. (being able to simply search for a location by name is great.) The maps and directions are all downloaded as you go from MapQuest, so it’s also a very lightweight download (“offline” GPS apps are often several gigabytes); the downside to that is that it won’t work if you don’t have a data connection.
MapQuest 4 Mobile isn’t as polished as Google Maps Navigation. It doesn’t rotate the map based on the direction you’re heading, no Street View, no search by voice, no traffic information. 
MapQuest 4 Mobile is a free download.
It’ll be interesting to see whether this competes at all (either in its current form or what it morphs into) with vehicle tracking systems in the future.
