Apple’s Jobs confirms iPhone ‘kill switch’ — Telegraph:

Phone differentiation used to be about radios and antennas and things like that,” Mr Jobs told the Wall Street Journal. “We think, going forward, the phone of the future will be differentiated by software.

From August 2008, soon after the launch of the App Store. To me, this is so obvious now. I wonder if it wasn't obvious back in 2008?

(Regarding the ‘kill switch’: I'm not aware that it has ever been used.)