Its better than nothing I suppose, but a better step might be to get manufacturers to build in hardware based cut offs of the transmission hardware and maybe hardwired LEDs showing when the mic/camera is active.
Forget LED's. Put in hardware disconnects for:
It'd be an entirely different phone, but it's not that crazy a thought. Push to talk was in widespread use by nextel folks for a long time, and also in CB and radio forever. I already start out every conference call I'm on by hitting mute... just make it easier to do that with a real button that actually ties to a circuit (maybe a slide, so I can slide it on/off). The others could also be put on one hardware airplane mode switch.