Pretty much all the dynos out there generate the same 3 V AC power. The iPhone needs 5 V DC to charge, so obviously that won't work as-is, although there are a number of connectors. The Schmidt hubs supposedly are more efficient, imposing less drag when on or off.

There is one hub I know of that puts out DC power; the same company also makes a converter to give you the standard USB power you want from other dynos. There are other companies as well making similar converters (the plug, zzing, ewerk)

Another option would be to get a battery extender for the phone.