Phones certainly don't have big enough capacitors to store enough power to run a radio. There's probably only a few pF of capacitance in an entire iPhone for example, though it not having an easily removable battery makes that a little moot.

I've had a look at a few teardowns but can't find another battery. My 'phone copes with the battery being removed while in offline mode so there's power somewhere.

But they probably do have enough power somewhere to silently turn themselves on, say briefly, according to some schedule or event. Not saying it's being done, but it could be done.

Where? No other components store power in any way. There's a few small capacitors lying around, but they're so small that you could never power anything from them. If something like this existed, people would have noticed a long, long time ago.

The "battery to keep your clock on time problem" was a problem of the offline PC world. Cellphones just need to get network time when they boot if they lost time. Thus manufacturers shouldn't need to include a separate clock battery in the limited space on a phone body.

Sorry, you're wrong.

Samsung Galaxy S1:

http://www.techinsights.com/uploadedImages/Public_Website/Co...

The internal battery is located at the top-right - a circular coin cell soldered to the board.

Samsung Galaxy S2:

http://i295.photobucket.com/albums/mm148/rprosperojr/IMG_120...

The internal battery is located at the center-top

Edit: In case of the SGS2 it's located next to the WLan/BT module.

That's no good. You might power your phone back on in an area without network coverage, or the signal might take too long to receive after power up, or you are running in flight mode on a plane, or ...

Basically, you still need a local clock.