GoldenGadgets.com has the Portable Hybrid Solar Charger for Blackberry, iPhone, Nokia, etc for $20 - 15% off with coupon code GGFA15 + $2 shipping = $19 shipped. Solar panels charge and maintain the built-in 2000 mah Lithium ion battery inside, providing USB spec power for your devices.
Nothing small electronics love more than hot sun.
#1 the solar panel charges the internal battery, then you use that to charge your small electronic device. No need for your iphone to get sunburned.
I was thinking they like gatorade after a hot day in the sun.
Would this be the most effective on the roof of a house or office building?
#2 In theory, yes, but you will quickly find that in order to maintain charger power it must stay in the sun.