While the Internet is generally accessible along the route (both via wireless and wifi) there are spots that don't have coverage and hotels/auberges/hostels that have limited to very bad coverage (particularly at times when all the pilgrims are on the same bandwidth). I carried both capabilities (phone and paper) and found that I used the paper more just because it was quicker to pull out and check while walking. When I finally got somewhere for the night, I used the phone app to plan out the next day and take a quick look at the route. As stated above, make sure that you review all the app/system settings to minimize the battery usage. That tends to be more of a problem than you might think (particularly if you're also using the phone to take pictures or play music (as a note, I thought I was going to do the later but ended up not listening to a note of music - listening to the world around me while walking or waiting was much more fun).