But basic voice calling should be possible with this modem itself.
Most modern modems (by "modern" I mean compared to the 2400bps Microteks we used to use back in the early 1990s) have audio handling through AT commands. Hypothetically it should be possible to write a program that captures audio from the modem, transcodes it and plays it through ALSA, as well as the reverse: capture ALSA audio, transcode it and play it back to the remote party through the modem.
Check this... http://search.cpan.org/~mukund/Ivrs-0.24/Ivrs.pm No further development, as these modems have almost vanished.
Warm Regards,
Mukund Deshmukh, Beta Computronics Pvt Ltd, 10/1 IT Park, Parsodi, Nagpur -440022, India.
Meet us at - K2010, Booth No. 12C40, 27th Oct - 3rd Nov 2010, Düsseldorf, Germany.