I just recently received the pedalpower+ universal-i-cable, which is a cable that purports to have circuitry allowing safe charging of all sorts of USB devices, including even the iPhone 3GS (a very finicky phone).
I took it on a quick ride today and my feelings are a bit mixed. It did work: my phone came up from 20% to 55%. On the other hand, since the ride was very much up and down, stop and start, the phone charging was constantly going on and off. This can't be good for the phone. The cutoff seems to be about 10 mph, which is faster than I usually go uphill. Now I don't know whether that's the cutoff where my iphone (3G, not the 3GS yet) will accept it, or a cutoff where the cable will provide it. I'd guess the former.
Friday I'll go on a longer ride and see how it works. I also have an imaxpower battery, which I could charge from the cable and (perhaps simultaneously) charge the phone from it. This approach would seem to be more friendly to the phone, while perhaps being less energy-efficient. Unfortunately, my battery is out of town until next week.
Anyone else have experience w/ this cable? The fit and finish all seems to be pretty good. The adapters etc. are relatively solid, and the bulky part of the cable appears waterproof.