Secure telephones

Bill Stewart bill.stewart at
Sun Jul 18 00:09:05 PDT 2004

>At 11:45 AM 7/17/2004, Thomas Shaddack wrote:
>>Pondering construction of a secure telephone. (Or at least a cellphone in
>>general. The user interfaces and features available on virtually all the
>>mass-market phones suck, to put it very very mildly, not even mentioning

If you're trying to build a usable cellphone,
you've got much more stringent design criteria than a deskphone.
You've got packaging requirements that force you into
serious industrial design if you want something pocket-sized
with good battery life, plus you've got to implement all the
cellular interface features.

If you're willing to build a backpack-phone, that's a lot simpler,
because you can use a laptop with a
[pick-your-favorite-cellular-data-standard] card
and either a wired headset or a Bluetooth frob for a BT headset.

An intermediate design, which other people have done,
is an 802.11 phone - take your favorite high-end multimedia PDA
and an 802.11 card and write whatever UI you want.
Again, you can either do a wire to your pocket or Bluetooth,
or do what some of the early Compaq Ipaq phones did and just
hold the thing up to your cheek.

I'm not aware of any cellular data cards in PDA-usable format
(unless you've got a PDA big enough for PCMCIA),
but you could take a GSM etc. phone with a wired interface to a PDA.

The fun UI to implement is an all-audio one, with speech recognition
for commands.  There's a lot of market space out there for that.
Bluetooth headsets aren't necessarily a great match for it,
because you're getting a low bit-rate signal from a cheap microphone,
as opposed to 11kHz 16-bit audio sampling. 

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