If you *need* GPS on your trip, a cell phone won't do. Cell phones have tiny GPS antennas compared to a standalone unit and make up for this in civilized areas by getting some help from the cell towers (this is called AGPS, assisted GPS). In the wilderness, even on flat ground, on a beautiful day, I've waited half an hour for my cell phone to get a GPS fix while stationary (eating lunch), which it only maintained for about 10 minutes once I started walking. There's also the battery life issue which is compounded by the long time to get a fix.
In terms of getting your coordinates, you can download specific Android apps that give you more low-level access to the GPS than the standard "maps" software which is included for navigation. I think the app I've used is called GPS Test and is free. It gives coordinates, the uncertainty (eg, "accurate to within 30 meters") lets you reset the AGPS data (which is supposed to help get an initial fix? Didn't seem to do much for me) and shows you how many satellites you're seeing and the signal strength of each one. The latter feature is nice if you're waiting for a fix, so you can see if you're likely to get one or if it's futile.
As a multipurpose device, a phone makes a pretty lightweight combination of camera, e-book, notepad (if you can stand typing on them for long), non-emergency communications, and *maybe* GPS, but you have to consider how you're going to manage the battery life on a multiday trip.