I am pretty sure I am talking about the device as a whole. I don't care for the exact reason that prevents me from running arbitrary software on it, be it hardware, software or even legalware ("you agree not to execute any unapproved software...").

It might even have a supercomputer hidden inside - as long as someone else decides what I run on it, it isn't a fully capable computer.

I think the issue is what you called the legalware. And I agree with you: the legalware on the iPhone prevents it form beeing a full-fledged personal computer. OTOH the OP has a point: the legalware on the iPhone is far less restrictive than the legalware on other cell-phones (and other closed hardware like playstations). Is it enough to talk of a quantum leap? Maybe yes.

Without software, the hardware is just a bunch of ICs. I don't see the point here.

Does the iphone have a USB port? Can I plug in my 19" monitor, keyboard, or mouse?

The iphone does have a connection point, and if I remember correctly, they are opening it up to third parties. So, if the phone can take blood pressure and insulin readings, I'm guessing it will only be a matter of time before it also accepts USB enabled devices. On a side note, I did see a pocket LED? projector (~$400) connected to this port on the iphone. It worked nicely.

It has a keyboard, pointing device, and display. Seems like a computer to me.