iPhone (not really a startup), NEST off the top of my head.
The iPhone wasn't in any way developed "in an area others dismiss". It was a huge market, with huge new competitors entering it (like Google).
It's the lack of mechanical keyboard that really differentiated it. They all had number pads or mechanical keyboards, because everyone dismissed it. Now none of them do. Even Google's early prototypes had mechanical keyboards. When Schmit took took the idea to Google, they switched to screen keyboards.