I've got a hub dynamo on my bike and will have on my new one (Koga Signature!!) I was looking to solve the same problem and found this:
http://bikeusbcharger.com/
Was about £10 i think - send the guy an email. I think that he had stopped making them, but he may well have some left for sale.
i found it excellent during last year’s touring. It gives a usb port which can be used to charge most things including an AA charger that I've got.
It doesn't need to be a hub dynamo - no reason why it can't be the tyre wall type.
Worth considering a hub dynamo on your next front wheel - very useful and great way to power lights - no worrying about batteries and the modern lights have capacitors in them so stay lit when stationary..
Here is another site I found when I was last looking:
http://www.rad-uk.com/bicycle-usb-charger-complete-version/
Ideal for a winter project - if that's your sort of thing.
The problem with modern phones with gps is the power requirements. I would suggest that even 8 hours is quite optimistic, but also it highlights the difficulty with integrated devices and cycle touring - once the battery goes flat you lose everything - phone, camera, music, gps etc.
It doesn't sound like you'll be too far from human life - maybe you're best bet is just to carry your charger and plug it in whenever you can. I can't imagine anyone refusing you some electric..
Whatever you do, I hope you enjoy the freedom of cycle touring.
Spencer