Let’s say I have to charge my iPhone 3gs completely every night. If I understand correctly from http://en.wikipedia.org/wiki/IPhone_3GS, that means I’m consuming
3.7 V * 1.219 Ah = 4.5 Wh. If I pay 10c / kWh for electricity (I generally pay less, but I think some parts of the country pay more, so I’ll go with that), it looks like my annual electricity costs to my cell phone are
4.5 Wh / 1000 * 10c * 365 ~= 16c.
Is my math right? That seems unbelievably cheap.