I didn't know what to expect, which is why I was testing. All of the desktop browsers on my machine do resolve the protocol-less URL in the address field though

I didn't know what to expect, which is why I was testing. All of the desktop browsers on my machine do resolve the protocol-less URL in the address field though (as HTTP). I mentioned it because I can see how it would be easy to notice that behavior on the desktop, see the same thing fail on an iPhone, and then assume that mobile Safari doesn't support these URLs at all.