Hmm...hardware secure phone?

[technopagan priest]

I've been reading up on Codecs.  Motorola has the MC145505 PCM Codec
which samples at 8khz and the PCM output is at 64kbps.  We can then
use the MC145532 ADPCM Transcoder to reduce the data stream to
16kbps.  With the breaks in spoken languages, perhaps we could get
this to compress just enough to go through a 14.4 kbps modem.

Anyway, who knows of a DES or RSA chip which will do 16kbps?
Then all we need is a microcontroller to run the show, and 
perform D-H or RSA key exchange.

-Thomas