With Cyclemeter (iPhone only), you can download any route from another source in GPX, TCX, FIT or KML format and save it as a Path rather than a workout (route). The GPS coordinates are stored in a local database on the phone. When you start your ride, you select the path and you can then follow it as you ride. Unfortunately, Cyclemeter doesn't offer turn-by-turn directions yet, but they say they are working on it. Once done with the ride, give the route a name and each time you select that route for a ride, it will use and display the route rather than the path. This will allow you to delete the path, if you wish to do so, and free up space in the database.