[_wmd]

As others have pointed out, the baseband is not your friend. Was thinking about this recently, and saw no reason why existing POCSAG (pager) networks couldn't be reused to provide a completely passive receiver. Imagine a phone where the baseband was off by default, unless attempting to make a call. Voicemail/e-mail summaries were broadcast encrypted via POCSAG, and generate notifications just like a new mail summary coming in via GPRS/3G would.

Obviously usability would suffer a little bit (mostly in huge latency when you actually wanted to make a call), but seems like very cheap phone could be built that integrated a pager, allowing complete disconnection from the 'active' radio network, avoiding location tracking by your cell provider, or similar evil tricks by third parties.

[this_user]

> " Imagine a phone where the baseband was off by default, unless attempting to make a call."

Except if everyone started using a phone like that, you wouldn't be able to call anyone.

[pyre]

You'd page them first!

[noselasd]

I'd imagine the POCSAG network would be quite overloaded, quite quickly. It doesn't have a lot of bandwidth, and unless the network knows where you are, messages destined to you would have to be broadcast everywhere.