You have to do more than turning it off (unless you can pop the battery). The FBI can bug a phone and have it send audio even while turned off, I'm guessing go the NSA can pretty much so what it wants.

http://news.cnet.com/2100-1029-6140191.html

Most modern phones take a long time to start up. Reminds of the time I had one of those Nokia phones. 2-3 seconds bootup time.

I think putting in Airplane Mode should be a good idea.

> I think putting in Airplane Mode should be a good idea.

And then you still would have to trust this Airplane Mode.

Honestly, I have absolutely no idea what is happening in my phone. Is it maybe still collecting data while it is in Airplane Mode and sending it somewhere once it is set back to regular mode? Or is it even sending data all the time, because the NSA knows that never a single plane has crashed because of active cellphones? Probably some smart people out there are checking their phone's internals and activities more than I do...

> You can choose to only sometimes carry a phone or turn it on.

Easier said than done. Unfortunately.