>> Why even take a smartphone on the trail anyways?
GPS, still camera, video camera, notepad, backup compass, evening reading, music/audio-books, apps that help with plant and animal recognition, apps for first aid or learning knots, route tracing, alarm clock... the list goes on and on. I'd take mine even if it didn't have a phone.
That said, the iPhone 4S is underwhelming. I don't mind the speed & performance of my 3GS. I'd love to have the faster chip and better camera, but it's not enough to induce iStupidity. I want a bigger screen, a more durable aluminum case, much longer battery life, and more power management options (widgets to shut off power-hungry features, on-demand under-clocking, simple band/frequency management & shut-off, etc), and the option to keep settings after a reboot (radio off).
In my dream world, I'd start adding some fun stuff (altimeter, barometer, thermometer with hi/low memory, laser pointer. The fun stuff wouldn't keep me from buying... but did I mention the super battery life?