It brings up a great conversation about the use of a cell phone as a valid source for mapping data (perhaps someone should start a new thread). We've all seen several news articles stating lost hikers were using a cell phone as their navigational device. I used to think "what a bonehead" but have recently changed my views on this subject.
I carry paper maps** and compass as my emergency source of navigation. They rarely come out of my backpack. I carry a GPSr as my (previous) primary source of navigation and found the TOPO maps I purchased (in 2004-2005) are severely outdated. It doesn't contain updated trailhead information or trail rerouting. This has frustrated me on several occasions with all the AT rerouting in Maine as my GPSr maps show the old trail location.
I've began using the free version of GaiaGPS and I found the maps much more accurate than both my paper copies and GPS however the free version was dependent on cell reception. I paid for a basic membership which allowed me to download multiple map sources to my phone (Apple) and doesn't rely on cell reception to pinpoint my location on the map(s). I've found it extremely accurate and it's surprisingly become my primary navigational aid.
Nothing is better than the self-reliance of understanding how to use a map and compass. However, the cell phone (as long as the battery is charged) is a really convenient and reliable navigational aid.
Note** My paper maps are printed from a free on-line resource such as CalTOPO or Acme Mapper and are not the maps provided in the AMC guide.
Now when I read an article that states a lost hiker was using a cell phone as their primary mapping source, I'm not so quick to eye roll at how unprepared they might be...