The SE w600i has one that you can. In fact, just yesterday I was using it outside (it was a gorgeous day) and could see the screen just fine. I think it uses some sort of reflective screen so that sunlight doesn't wash it out. I say this because you can't see the backlight in the sun (obviously) but the pixels are still visible because the sun provides the light.
iPods use a semi-reflective screen, which is why you can see them just fine (readable but poor color accuracy) in bright sunlight with the backlight not even needed. (Compared to a laptop whose screen looks 95% black in strong light.) I assume the iPhone will work the same way.
The reason some devices do NOT use this kind of screen is that it makes the backlight dimmer--less light gets though from behind. Not good for a laptop.