ofxiOS is built on top of ofxiPhone. It allows developers to build native iPhone apps and embed OF apps only when needed.
This is different to ofxiPhone which sets up the OF app at the root of the iPhone application, which means that the iPhone application launches straight into the OF app but what if you wanted some native iOS UI before then?
ofxiOS allows to embed multiple OF apps at different levels in the iPhone application and enables developers to make iPhone applications as they normally would but with the added benefit of having OpenFrameworks at their disposal.