Re: Neil Barnes Switching off phones does not disable built-in GPS functionality
A GPS does not "wake itself or stay continually on in the background" - the "fast GPS lock" you're describing is called "hot start" and is a result of the GPS not having to download the almanac (of satellite location) when powered up, which takes several minutes.
A battery backup on the GPS isn't used to wake the GPS, it's simply to keep the almanac in memory. That's why the draw when in this standby mode is in the nanoamps. I don't have first hand knowledge of the GPS chip inside smartphones, but I'd be surprised if they didn't work this way simply because there's no need for them to - Apple will be buying commodity GPS chips, and this is how they're usually(*) designed.
There's an easy way to check - turn off your phone, take a plane flight to the other side of the world and turn it on. If it gets a GPS lock within a few seconds, it's been surreptitiously powering itself up to track its location. If it takes a few minutes, as I expect it will, then the GPS has found its almanac no longer applies and has downloaded a new one.
However, Matt, you/re right that the GPS is not a power hungry device, again it's a few tens of milliamps normally.
(*) putting my neck out here, but I've yet to see one that isn't.