I found some test data on dynamos in this thread. As far as dynamos online, I've found the Dymotec 6, which is, unsurprisingly, a 6-volt source.
Evidently all dynamos are AC, and need to be rectified to get to DC (and then maybe "smoothed") before use.

Another random comment I found on the web says that USB is 5 volts, meaning that the current probably needs to be limited somewhere before it gets to the iphone. And another comment says "CONNECTING YOUR PHONE DIRECTLY TO THE DYNAMO WILL DAMAGE YOUR PHONE". Probably true.

A side-wall generator and something like the PedalPower+ sounds good, but they don't even have prices online. Anything similar in this hemisphere?

This sounds like it just needs very simple circuitry. Why isn't it widespread?