Most cell phones today are charged via a mini-USB connection, runs at around 0.5 amps at ~5V.
This has several advantages because now charging your phone or an ipod can be quite easily achieved as long as you have a female USB port.
For those of you who are back country enthusiasts or just interested in something that's simple and self-rewarding to make - this is perfect for you.
A flexible rollable extreemly lightweight solar powered trickle charger.
Build a solar iPod charger
Absolutely brilliant.