Margaret - A problem with cell phones is that they will lose coverage then regain it often in a trail environment. Each time that happens, a lot of power is consumed by searching for and switching towers. In addition, smartphones are constantly getting e-mail pushed to them and that eats some power as well. Even when they are turned off, some power is being used. I would suggest that you remove the battery when you aren’t using it to make it last longer.
Most of the gps programs for smart phones do not place the maps on the phone, but downlod them in real time via the internet. If you are in a no-service area, the proper maps won’t be installed. If you could find a program that can be set up so the desired maps are pre-loaded on the phone that would be a plus.
Here is a link to a bunch of programs for Blackberry GPS:
http://blackberry.handmark.com/c/325/GPSMapping
Have a great hike - I’d be interested in hearing how the phone gps works for you.
bearcreek