I have one of these for camping:
It's a great radio that comes with a mechanism for powering USB devices via a hand crank.
So not only would I have the possibility of using 4G all day, I'll have the most forearm straight of any EVO owner out there. :P
It also comes with a solar charger, but sadly it only works for the internal battery and not the external usb port.
I think we need to find the most powerful Solar Powered USB charger ASAP. It's possibly the only alternative to tethering ourselves to a wall outlet and extra batteries.
I saw a Solio display at CES this year and they claimed to be "The Best", but are there any Solar charger users out there can who can claim better?