There's a script I wrote in voice/pvftools called "extract_gsm" that
extracts the GSM data from a US Robotics "rmd" file.  Once you have
that, and you have a version of "sox" that can convert .gsm files in
to .au (or other format) files, you're in business.

I found the necessary patches for sox after a bit of digging:

  http://kbs.cs.tu-berlin.de/~jutta/toast.html

You'll need the GSM library before you try to apply the sox patches.
It's too bad sox doesn't come with GSM support--it seems to have
about everything else...

Also, Thomas Hellstroem (thomas@vtd.volvo.se) had some C programs to
extract GSM data and to "pack" GSM data into rmd files off of his page.
Unforutnately, I didn't save the URL.

 -Scott Hutton, UCS Messaging Team, Indiana Univeristy