Thanks guys, I’m still not sure I’m explaining this right.
With an App like a browser, preference for portrait/landscape depends on the website being viewed so such Apps will support both and the user will rotate as appropriate.
At the other extreme, the ‘phone App’ itself, with the dialling number pad, is clearly optimised for portrait and I suspect everybody is happy with that. But the phone App is a bit special because it also has to suit the physical layout of microphone and speaker.
So, providing an iPhone App can be clearly optimised for portrait with absolutely no compromises, are people happy to be forced to use it that way? Or will you sometimes want to use landscape for that App even though it doesn’t work so well, just because you like holding the phone sideways?